diff --git a/CHANGELOG.md b/CHANGELOG.md
index 858a9e8..22c08a6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,28 @@ All notable changes to this project will be documented in this file.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
+## [2.6.0] - 2026-06
+
+Release rollup of 2.5.2–2.5.8 (reversible initials, instance tracking fixes,
+live `MASK_*` flags, O(n) replacements, threat model docs, stderr passwords).
+
+### Changed
+- Version strings synchronized across all file headers (were stuck at 2.5.1)
+- Historical "extracted during vX refactoring" phrases pinned to v2.5.0
+  so they no longer drift with version bumps
+
+## [2.5.8] - 2026-06
+
+### Performance
+- Replacement loops (mask engine, initials phase, both unmask passes) build
+  the result via segment join instead of rebuilding the whole string per
+  replacement — O(n) instead of O(n²) on large documents
+
+### Fixed
+- Mask engine processes items in document order: instance numbers now match
+  occurrence order (was reverse — wrong original could be restored when two
+  different values masked to the same string)
+
 ## [2.5.7] - 2026-06
 
 ### Security
diff --git a/config_example.py b/config_example.py
index 51824ac..50116a4 100644
--- a/config_example.py
+++ b/config_example.py
@@ -1,7 +1,7 @@
 #!/usr/bin/env python3
 # -*- coding: utf-8 -*-
 """
-Configuration example for data_masking.py v2.5.1
+Configuration example for data_masking.py v2.6.0
 
 Demonstrates all available configuration options using dataclasses.
 No external dependencies required — uses only Python standard library.
@@ -9,7 +9,7 @@
 Author: Vladyslav V. Prodan
 Contact: github.com/click0
 Phone: +38(099)6053340
-Version: 2.5.1
+Version: 2.6.0
 License: BSD 3-Clause "New" or "Revised" License
 Year: 2025-2026
 """
@@ -25,7 +25,7 @@
 @dataclass
 class SystemConfig:
     """Системні налаштування."""
-    version: str = "v2.5.1"
+    version: str = "v2.6.0"
     hash_algorithm: str = "blake2b"
     hash_digest_size: int = 8
     encoding: str = "utf-8"
@@ -172,7 +172,7 @@ def to_dict(self) -> dict:
     data = config.to_dict()
 
     print("=" * 70)
-    print("  Data Masking Configuration Example v2.5.1")
+    print("  Data Masking Configuration Example v2.6.0")
     print("=" * 70)
 
     for section_name, section_data in data.items():
diff --git a/config_example.yaml b/config_example.yaml
index 8d95e33..91025c2 100644
--- a/config_example.yaml
+++ b/config_example.yaml
@@ -1,5 +1,5 @@
 # ==========================================================================
-# Приклад конфігурації для системи маскування даних v2.5.1
+# Приклад конфігурації для системи маскування даних v2.6.0
 #
 # Скопіюйте цей файл як config.yaml та налаштуйте під свої потреби.
 # Згенерувати конфігурацію за замовчуванням:
@@ -8,7 +8,7 @@
 # Author: Vladyslav V. Prodan
 # Contact: github.com/click0
 # Phone: +38(099)6053340
-# Version: 2.5.1
+# Version: 2.6.0
 # License: BSD 3-Clause "New" or "Revised" License
 # Year: 2025-2026
 # ==========================================================================
@@ -18,7 +18,7 @@
 # --------------------------------------------------------------------------
 system:
   # Версія конфігурації (для сумісності)
-  version: "v2.5.1"
+  version: "v2.6.0"
 
   # Алгоритм хешування для детерміністичного маскування.
   # Той самий вхід завжди дає той самий замаскований результат.
diff --git a/data_masking.py b/data_masking.py
index 685b243..b8d1665 100644
--- a/data_masking.py
+++ b/data_masking.py
@@ -2,19 +2,26 @@
 # -*- coding: utf-8 -*-
 
 """
-Data Masking Script v2.5.1
+Data Masking Script v2.6.0
 Локально узгоджене маскування конфіденційних даних з INSTANCE TRACKING
 
-ОНОВЛЕНО В v2.5.1:
-- Рефакторинг: розбито на пакет masking/ (constants, helpers, language,
-  context, mask_personal, mask_military, engine, cli)
-- Додано __main__.py: запуск з кореня репо — python . mask / python . unmask
-- Зворотна сумісність: всі імпорти з data_masking продовжують працювати
+ОНОВЛЕНО В v2.6.0:
+- Зворотні ініціали: ПІБ типу "Іванов П.А." зберігаються у mapping
+  (категорія initials) та повністю відновлюються при unmask
+- Instance tracking у порядку документа; повторні текстові дати
+  відновлюються всі
+- "Живі" прапорці MASK_*: data_masking.MASK_NAMES = False знову діє
+- O(n) заміни замість O(n^2) на великих файлах
+- Згенеровані паролі виводяться у stderr
+
+Архітектура (з v2.5.0): тонка обгортка над пакетом masking/
+(constants, helpers, language, context, mask_personal, mask_military,
+engine, cli); запуск з кореня репо — python . mask / python . unmask
 
 Author: Vladyslav V. Prodan
 Contact: github.com/click0
 Phone: +38(099)6053340
-Version: 2.5.1
+Version: 2.6.0
 License: BSD 3-Clause "New" or "Revised" License
 Year: 2025-2026
 """
@@ -23,7 +30,7 @@
 # Re-exports from masking package for backward compatibility
 # ============================================================================
 
-__version__ = "2.5.7"
+__version__ = "2.6.0"
 
 from masking.constants import (
     __version__, __author__, __contact__, __phone__, __license__, __year__,
diff --git a/diagnose_mapping.py b/diagnose_mapping.py
index 0d3b553..9f9a1d5 100644
--- a/diagnose_mapping.py
+++ b/diagnose_mapping.py
@@ -6,7 +6,7 @@
 Author: Vladyslav V. Prodan
 Contact: github.com/click0
 Phone: +38(099)6053340
-Version: 2.5.1
+Version: 2.6.0
 License: BSD 3-Clause "New" or "Revised" License
 Year: 2025-2026
 
diff --git a/masking/__init__.py b/masking/__init__.py
index 589e3bd..3d4fe34 100644
--- a/masking/__init__.py
+++ b/masking/__init__.py
@@ -4,7 +4,7 @@
 """
 Masking package — data masking with instance tracking.
 
-Refactored from monolithic data_masking.py in v2.5.1.
+Refactored from monolithic data_masking.py (v2.5.0).
 """
 
 from masking.constants import __version__, __author__, __contact__, __license__, __year__
diff --git a/masking/cli.py b/masking/cli.py
index 555d853..4b7d42d 100644
--- a/masking/cli.py
+++ b/masking/cli.py
@@ -4,7 +4,7 @@
 """
 CLI entry point and orchestration for data masking.
 
-Extracted from data_masking.py during v2.5.1 refactoring.
+Extracted from data_masking.py during the package refactoring (v2.5.0).
 """
 
 import json
diff --git a/masking/constants.py b/masking/constants.py
index f541b37..06af580 100644
--- a/masking/constants.py
+++ b/masking/constants.py
@@ -4,7 +4,7 @@
 """
 Masking constants, patterns, and configuration flags.
 
-Extracted from data_masking.py during v2.5.1 refactoring.
+Extracted from data_masking.py during the package refactoring (v2.5.0).
 """
 
 import re
@@ -26,7 +26,7 @@
 # ============================================================================
 # МЕТАДАНІ
 # ============================================================================
-__version__ = "2.5.7"
+__version__ = "2.6.0"
 __author__ = "Vladyslav V. Prodan"
 __contact__ = "github.com/click0"
 __phone__ = "+38(099)6053340"
diff --git a/masking/context.py b/masking/context.py
index 25b55d3..82bbdaa 100644
--- a/masking/context.py
+++ b/masking/context.py
@@ -4,7 +4,7 @@
 """
 Context analysis and line parsing functions.
 
-Extracted from data_masking.py during v2.5.1 refactoring.
+Extracted from data_masking.py during the package refactoring (v2.5.0).
 """
 
 import re
diff --git a/masking/engine.py b/masking/engine.py
index 5e27941..b7a424d 100644
--- a/masking/engine.py
+++ b/masking/engine.py
@@ -4,7 +4,7 @@
 """
 Main masking engine: context-aware text masking and JSON processing.
 
-Extracted from data_masking.py during v2.5.1 refactoring.
+Extracted from data_masking.py during the package refactoring (v2.5.0).
 """
 
 import random
@@ -133,10 +133,12 @@ def _mask_initials_pib(text: str, masking_dict: Dict, instance_counters: Dict) -
         if not any(c[0] < k[1] and c[1] > k[0] for k in kept):
             kept.append(c)
 
-    # Фаза 2: у порядку документа маскуємо та записуємо mapping
+    # Фаза 2: у порядку документа маскуємо, записуємо mapping
+    # і збираємо результат сегментами (O(n))
     masking_dict["mappings"].setdefault("initials", {})
     kept.sort(key=lambda x: x[0])
-    replacements = []
+    segments = []
+    prev_end = 0
     for start, end, surname, initials, has_space, ini_first in kept:
         ms = mask_surname(surname, masking_dict, instance_counters)
         sep = '. ' if has_space else '.'
@@ -147,11 +149,13 @@ def _mask_initials_pib(text: str, masking_dict: Dict, instance_counters: Dict) -
         masked_ini = add_to_mapping(masking_dict, instance_counters,
                                     "initials", orig_ini, masked_ini)
         new_text = f"{masked_ini} {ms}" if ini_first else f"{ms} {masked_ini}"
-        replacements.append((start, end, new_text))
+        segments.append(text[prev_end:start])
+        segments.append(new_text)
+        prev_end = end
 
-    # Заміни з кінця тексту, щоб не збити позиції
-    for start, end, new_text in reversed(replacements):
-        text = text[:start] + new_text + text[end:]
+    if segments:
+        segments.append(text[prev_end:])
+        text = ''.join(segments)
 
     return text
 
@@ -265,43 +269,46 @@ def mask_text_context_aware(text: str, masking_dict: Dict, instance_counters: Di
             if not skip:
                 items_to_mask.append({'type': 'date_text', 'full_text': match.group(0), 'number_part': match.group(0), 'start': match.start(), 'end': match.end()})
 
-    items_to_mask.sort(key=lambda x: x['start'], reverse=True)
+    # Обхід у порядку документа: instance tracking збігається з порядком
+    # входжень (потрібно для unmask), а заміни збираються сегментами —
+    # O(n) замість квадратичного text[:i] + ... + text[j:] на кожен елемент
+    items_to_mask.sort(key=lambda x: x['start'])
 
+    segments = []
+    prev_end = 0
     for item in items_to_mask:
-        masked = ""
+        if item['start'] < prev_end: continue  # перекриття — пропускаємо
         if text[item['start']:item['end']] != item['full_text']: continue
-        if item['type'] == 'ipn': masked = mask_ipn(item['number_part'], masking_dict, instance_counters)
-        elif item['type'] == 'passport_id': masked = mask_passport_id(item['number_part'], masking_dict, instance_counters)
-        elif item['type'] == 'military_id': masked = mask_military_id(item['number_part'], masking_dict, instance_counters)
-        elif item['type'] == 'military_unit': masked = mask_military_unit(item['number_part'], masking_dict, instance_counters)
+
+        replacement = None
+        if item['type'] == 'ipn': replacement = mask_ipn(item['number_part'], masking_dict, instance_counters)
+        elif item['type'] == 'passport_id': replacement = mask_passport_id(item['number_part'], masking_dict, instance_counters)
+        elif item['type'] == 'military_id': replacement = mask_military_id(item['number_part'], masking_dict, instance_counters)
+        elif item['type'] == 'military_unit': replacement = mask_military_unit(item['number_part'], masking_dict, instance_counters)
         elif item['type'] == 'brigade_number':
-            masked = mask_brigade_number(item['full_text'], masking_dict, instance_counters)
-            text = text[:item['start']] + masked + text[item['end']:]
-            continue
+            replacement = mask_brigade_number(item['full_text'], masking_dict, instance_counters)
         elif item['type'] == 'date':
-            masked = mask_date(item['full_text'], masking_dict, instance_counters)
-            text = text[:item['start']] + masked + text[item['end']:]
-            continue
+            replacement = mask_date(item['full_text'], masking_dict, instance_counters)
         elif item['type'] == 'date_text':
-            masked = _mask_date_text(item['full_text'], masking_dict, instance_counters)
-            text = text[:item['start']] + masked + text[item['end']:]
-            continue
+            replacement = _mask_date_text(item['full_text'], masking_dict, instance_counters)
         elif item['type'] == 'order_simple':
             masked = mask_order_number(item['number_part'], masking_dict, instance_counters)
-            new_full = item['full_text'].replace(item['number_part'], masked, 1)
-            text = text[:item['start']] + new_full + text[item['end']:]
-            continue
+            replacement = item['full_text'].replace(item['number_part'], masked, 1)
         elif item['type'] == 'order_with_letters':
             masked = mask_order_number_with_letters(item['number_part'], masking_dict, instance_counters)
-            new_full = item['full_text'].replace(item['number_part'], masked, 1)
-            text = text[:item['start']] + new_full + text[item['end']:]
-            continue
+            replacement = item['full_text'].replace(item['number_part'], masked, 1)
         elif item['type'] in ['br_complex', 'br_with_slashes', 'br_with_suffix', 'br_standalone']:
-            masked = mask_br_number(item['full_text'], masking_dict, instance_counters)
-            text = text[:item['start']] + masked + text[item['end']:]
+            replacement = mask_br_number(item['full_text'], masking_dict, instance_counters)
+
+        if replacement is None or replacement == "":
             continue
+        segments.append(text[prev_end:item['start']])
+        segments.append(replacement)
+        prev_end = item['end']
 
-        if masked: text = text[:item['start']] + masked + text[item['end']:]
+    if segments:
+        segments.append(text[prev_end:])
+        text = ''.join(segments)
 
     lines = text.split('\n')
     masked_lines = []
diff --git a/masking/helpers.py b/masking/helpers.py
index 40e93fd..c749f25 100644
--- a/masking/helpers.py
+++ b/masking/helpers.py
@@ -4,7 +4,7 @@
 """
 Base helper functions for masking operations.
 
-Extracted from data_masking.py during v2.5.1 refactoring.
+Extracted from data_masking.py during the package refactoring (v2.5.0).
 """
 
 import hashlib
diff --git a/masking/language.py b/masking/language.py
index 49ce211..f7d2767 100644
--- a/masking/language.py
+++ b/masking/language.py
@@ -4,7 +4,7 @@
 """
 Language analysis functions: gender detection, grammatical case, declension.
 
-Extracted from data_masking.py during v2.5.1 refactoring.
+Extracted from data_masking.py during the package refactoring (v2.5.0).
 """
 
 import random
diff --git a/masking/mask_military.py b/masking/mask_military.py
index 01d59cc..042e7b9 100644
--- a/masking/mask_military.py
+++ b/masking/mask_military.py
@@ -4,7 +4,7 @@
 """
 Military data masking: ranks, units, orders, BR numbers, dates.
 
-Extracted from data_masking.py during v2.5.1 refactoring.
+Extracted from data_masking.py during the package refactoring (v2.5.0).
 """
 
 import random
diff --git a/masking/mask_personal.py b/masking/mask_personal.py
index 5d7e328..4bac0f5 100644
--- a/masking/mask_personal.py
+++ b/masking/mask_personal.py
@@ -4,7 +4,7 @@
 """
 Personal data masking functions: IPN, passport, military ID, names.
 
-Extracted from data_masking.py during v2.5.1 refactoring.
+Extracted from data_masking.py during the package refactoring (v2.5.0).
 """
 
 import random
diff --git a/modules/__init__.py b/modules/__init__.py
index 2bcf3fc..fac6c03 100644
--- a/modules/__init__.py
+++ b/modules/__init__.py
@@ -2,7 +2,7 @@
 # -*- coding: utf-8 -*-
 
 """
-Data Masking Modules Package v2.5.1
+Data Masking Modules Package v2.6.0
 
 Модулі системи маскування даних.
 """
diff --git a/modules/config.py b/modules/config.py
index 6aeb630..36b2741 100644
--- a/modules/config.py
+++ b/modules/config.py
@@ -2,7 +2,7 @@
 # -*- coding: utf-8 -*-
 
 """
-Configuration Module v2.5.1 for data_masking.py
+Configuration Module v2.6.0 for data_masking.py
 
 Provides YAML + ENV + CLI configuration loading with priority resolution:
     CLI > ENV > config.yaml > config.py > Default
@@ -16,7 +16,7 @@
 Year: 2025-2026
 """
 
-__version__ = "2.5.1"
+__version__ = "2.6.0"
 
 import os
 import logging
diff --git a/modules/masking_logger.py b/modules/masking_logger.py
index d0d3861..08cc9e3 100644
--- a/modules/masking_logger.py
+++ b/modules/masking_logger.py
@@ -2,7 +2,7 @@
 # -*- coding: utf-8 -*-
 
 """
-Logging Module v2.5.1 for data_masking.py
+Logging Module v2.6.0 for data_masking.py
 
 Provides structured logging with JSON and colored console output
 for masking operations.
@@ -22,7 +22,7 @@
 from typing import Any, Dict, Optional
 
 
-__version__ = "2.5.1"
+__version__ = "2.6.0"
 
 
 class JsonFormatter(logging.Formatter):
diff --git a/modules/password_generator.py b/modules/password_generator.py
index e14ef39..2fe019c 100644
--- a/modules/password_generator.py
+++ b/modules/password_generator.py
@@ -1,7 +1,7 @@
 #!/usr/bin/env python3
 # -*- coding: utf-8 -*-
 """
-Password Generator Module v2.5.1
+Password Generator Module v2.6.0
 Генератор паролів з підтримкою ASCII, кирилиці та кастомних символів.
 Використання як модуль:
     from password_generator import generate_password, PasswordConfig
@@ -25,7 +25,7 @@
 Author: Vladyslav V. Prodan
 Contact: github.com/click0
 Phone: +38(099)6053340
-Version: 2.5.1
+Version: 2.6.0
 License: BSD 3-Clause "New" or "Revised" License
 Year: 2025-2026
 """
@@ -34,7 +34,7 @@
 import argparse
 from dataclasses import dataclass
 from typing import Optional, List, Dict, Any, Union
-__version__ = "2.5.1"
+__version__ = "2.6.0"
 __author__ = "Vladyslav V. Prodan"
 # =============================================================================
 # КОНСТАНТИ
diff --git a/modules/re_mask.py b/modules/re_mask.py
index 0457716..e70780b 100644
--- a/modules/re_mask.py
+++ b/modules/re_mask.py
@@ -2,7 +2,7 @@
 # -*- coding: utf-8 -*-
 
 """
-Re-Masking Module v2.5.1
+Re-Masking Module v2.6.0
 Multi-pass masking with chain tracking for data_masking.py
 
 Provides:
@@ -12,7 +12,7 @@
 
 Chain JSON format:
     {
-        "version": "2.5.1",
+        "version": "2.6.0",
         "chain_id": "<sha256_hash[:12]>",
         "chain_version": 2,
         "created_at": "ISO-8601",
@@ -38,7 +38,7 @@
 from pathlib import Path
 from typing import Any, Callable, Dict, List, Optional, Tuple
 
-__version__ = "2.5.1"
+__version__ = "2.6.0"
 
 # Standard mapping categories used by data_masking.py
 MAPPING_CATEGORIES = [
@@ -49,7 +49,7 @@
 ]
 
 
-def make_empty_masking_dict(version: str = "2.5.1") -> Dict:
+def make_empty_masking_dict(version: str = "2.6.0") -> Dict:
     """Create a fresh empty masking dict with all required category keys.
 
     Args:
diff --git a/modules/security.py b/modules/security.py
index c7d0ef9..ce6a464 100644
--- a/modules/security.py
+++ b/modules/security.py
@@ -2,7 +2,7 @@
 # -*- coding: utf-8 -*-
 
 """
-Security Module v2.5.1
+Security Module v2.6.0
 
 Provides AES-256-GCM encryption/decryption of mapping files
 for data_masking.py.
@@ -15,7 +15,7 @@
 Year: 2025-2026
 """
 
-__version__ = "2.5.1"
+__version__ = "2.6.0"
 
 import json
 import os
diff --git a/modules/selective.py b/modules/selective.py
index dbea7ca..e8a6f7e 100644
--- a/modules/selective.py
+++ b/modules/selective.py
@@ -2,7 +2,7 @@
 # -*- coding: utf-8 -*-
 
 """
-Selective Masking Module v2.5.1
+Selective Masking Module v2.6.0
 
 Provides --only / --exclude support: mask only selected data types.
 Supports type aliases (plural forms, Ukrainian names), type groups,
@@ -19,7 +19,7 @@
 from dataclasses import dataclass, field
 from typing import Dict, List, Optional, Set
 
-__version__ = "2.5.1"
+__version__ = "2.6.0"
 
 # ============================================================================
 # AVAILABLE TYPES
diff --git a/modules/tools.py b/modules/tools.py
index f3bac64..25e81a5 100644
--- a/modules/tools.py
+++ b/modules/tools.py
@@ -2,7 +2,7 @@
 # -*- coding: utf-8 -*-
 
 """
-Tools API Module v2.5.1
+Tools API Module v2.6.0
 
 Provides atomic masking functions for programmatic use (without CLI).
 Each function is self-contained and operates on a single value, updating
@@ -52,7 +52,7 @@
 # ============================================================================
 # METADATA
 # ============================================================================
-__version__ = "2.5.1"
+__version__ = "2.6.0"
 __author__ = "Vladyslav V. Prodan"
 __contact__ = "github.com/click0"
 __license__ = "BSD 3-Clause"
diff --git a/requirements.txt b/requirements.txt
index b5e133a..098a378 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,4 +1,4 @@
-# Data Masking System v2.5.1
+# Data Masking System v2.6.0
 # Python 3.9+
 
 # Генерація реалістичних українських імен
diff --git a/tests/test_case_preservation.py b/tests/test_case_preservation.py
index 31a4188..afab947 100644
--- a/tests/test_case_preservation.py
+++ b/tests/test_case_preservation.py
@@ -5,7 +5,7 @@
 Author: Vladyslav V. Prodan
 Contact: github.com/click0
 Phone: +38(099)6053340
-Version: 2.5.1
+Version: 2.6.0
 License: BSD 3-Clause "New" or "Revised" License
 Year: 2025-2026
 
diff --git a/tests/test_diagnose.py b/tests/test_diagnose.py
index 2468eef..7bceadb 100644
--- a/tests/test_diagnose.py
+++ b/tests/test_diagnose.py
@@ -6,7 +6,7 @@
 Author: Vladyslav V. Prodan
 Contact: github.com/click0
 Phone: +38(099)6053340
-Version: 2.5.1
+Version: 2.6.0
 License: BSD 3-Clause "New" or "Revised" License
 Year: 2025-2026
 """
diff --git a/tests/test_helpers.py b/tests/test_helpers.py
index 3cbb88c..c31f209 100644
--- a/tests/test_helpers.py
+++ b/tests/test_helpers.py
@@ -5,7 +5,7 @@
 Author: Vladyslav V. Prodan
 Contact: github.com/click0
 Phone: +38(099)6053340
-Version: 2.5.1
+Version: 2.6.0
 License: BSD 3-Clause "New" or "Revised" License
 Year: 2025-2026
 
diff --git a/tests/test_initials.py b/tests/test_initials.py
index a761f95..c0fe50e 100644
--- a/tests/test_initials.py
+++ b/tests/test_initials.py
@@ -135,3 +135,26 @@ def test_roundtrip_repeated_person(self):
         version = check_mapping_version(masking_dict)
         restored, _ = unmask_text_v2(masked, masking_dict, version)
         assert restored == text
+
+
+class TestLargeDocumentRoundtrip:
+    """Великий документ: instance tracking у порядку документа,
+    сегментна збірка замін не губить і не дублює текст."""
+
+    def test_many_items_roundtrip(self):
+        import random as rnd
+        rnd.seed(42)
+        lines = []
+        for i in range(300):
+            ipn = ''.join(rnd.choice('0123456789') for _ in range(10))
+            day = rnd.randint(1, 28)
+            lines.append(
+                f'Запис {i}: ІПН {ipn} від {day:02d}.03.2024, в/ч А{rnd.randint(1000, 9999)}'
+            )
+        text = '\n'.join(lines)
+
+        masked, masking_dict = mask(text)
+        assert masked != text
+        version = check_mapping_version(masking_dict)
+        restored, _ = unmask_text_v2(masked, masking_dict, version)
+        assert restored == text
diff --git a/tests/test_integration.py b/tests/test_integration.py
index d5dcea2..3ea060f 100644
--- a/tests/test_integration.py
+++ b/tests/test_integration.py
@@ -1,7 +1,7 @@
 #!/usr/bin/env python3
 # -*- coding: utf-8 -*-
 """
-Інтеграційні тести для data_masking.py v2.5.1
+Інтеграційні тести для data_masking.py v2.6.0
 Тестує нові функції:
 - --init-config
 - --encrypt / --password
@@ -11,7 +11,7 @@
 Author: Vladyslav V. Prodan
 Contact: github.com/click0
 Phone: +38(099)6053340
-Version: 2.5.1
+Version: 2.6.0
 License: BSD 3-Clause "New" or "Revised" License
 Year: 2025-2026
 """
@@ -574,7 +574,7 @@ def test_basic_masking(self, sample_input_file, temp_dir, run_masking):
 
             text = sample_input_file.read_text(encoding="utf-8")
             masking_dict = {
-                "version": "2.5.1",
+                "version": "2.6.0",
                 "mappings": {k: {} for k in [
                     "ipn", "passport_id", "military_id", "surname", "name",
                     "military_unit", "order_number", "order_number_with_letters",
@@ -608,7 +608,7 @@ def test_masking_with_only_flag(self, sample_input_file, temp_dir):
 
         # Симуляція --only ipn (маскуємо тільки ІПН)
         masking_dict = {
-            "version": "2.5.1",
+            "version": "2.6.0",
             "mappings": {k: {} for k in [
                 "ipn", "passport_id", "military_id", "surname", "name",
                 "military_unit", "order_number", "rank", "date", "date_text", "patronymic"
@@ -648,7 +648,7 @@ def test_masking_with_remask(self, sample_input_file, temp_dir, run_masking):
             text = sample_input_file.read_text(encoding="utf-8")
 
             masking_dict = {
-                "version": "2.5.1",
+                "version": "2.6.0",
                 "mappings": {k: {} for k in [
                     "ipn", "passport_id", "military_id", "surname", "name",
                     "military_unit", "order_number", "order_number_with_letters",
@@ -701,7 +701,7 @@ def test_text_date_masking(self, temp_dir):
         text = 'від "06" жовтня 2025 року №292'
 
         masking_dict = {
-            "version": "2.5.1",
+            "version": "2.6.0",
             "mappings": {k: {} for k in [
                 "ipn", "passport_id", "military_id", "surname", "name",
                 "order_number", "rank", "date", "date_text", "patronymic"
@@ -724,7 +724,7 @@ def test_numeric_date_masking(self, temp_dir):
         text = "Дата: 15.03.2024"
 
         masking_dict = {
-            "version": "2.5.1",
+            "version": "2.6.0",
             "mappings": {k: {} for k in [
                 "ipn", "passport_id", "military_id", "surname", "name",
                 "order_number", "rank", "date", "date_text", "patronymic"
@@ -765,7 +765,7 @@ def test_no_report_flag(self, temp_dir):
         # Симулюємо --no-report
         text = "Тестовий текст"
         masking_dict = {
-            "version": "2.5.1",
+            "version": "2.6.0",
             "mappings": {"surname": {}, "name": {}},
             "statistics": {},
             "instance_tracking": {}
@@ -800,7 +800,7 @@ def test_json_output(self, temp_dir):
         }
 
         masking_dict = {
-            "version": "2.5.1",
+            "version": "2.6.0",
             "mappings": {k: {} for k in [
                 "ipn", "passport_id", "surname", "name", "rank", "patronymic"
             ]},
@@ -881,7 +881,7 @@ class TestChainRoundtrip:
     def _make_masking_dict(self):
         """Create a fresh masking dict."""
         from re_mask import make_empty_masking_dict
-        return make_empty_masking_dict("2.5.1")
+        return make_empty_masking_dict("2.6.0")
 
     def test_chain_roundtrip_2_passes(self):
         """Тест: маскування у 2 проходи, потім відновлення через ланцюг."""
diff --git a/tests/test_patronymic.py b/tests/test_patronymic.py
index b936e03..96c8833 100644
--- a/tests/test_patronymic.py
+++ b/tests/test_patronymic.py
@@ -5,7 +5,7 @@
 Author: Vladyslav V. Prodan
 Contact: github.com/click0
 Phone: +38(099)6053340
-Version: 2.5.1
+Version: 2.6.0
 License: BSD 3-Clause "New" or "Revised" License
 Year: 2025-2026
 
diff --git a/tests/test_rank_data.py b/tests/test_rank_data.py
index e1163ea..c849c3a 100644
--- a/tests/test_rank_data.py
+++ b/tests/test_rank_data.py
@@ -7,7 +7,7 @@
 Author: Vladyslav V. Prodan
 Contact: github.com/click0
 Phone: +38(099)6053340
-Version: 2.5.1
+Version: 2.6.0
 License: BSD 3-Clause "New" or "Revised" License
 Year: 2025-2026
 
diff --git a/tests/test_unmask.py b/tests/test_unmask.py
index a847971..e4435c4 100644
--- a/tests/test_unmask.py
+++ b/tests/test_unmask.py
@@ -6,7 +6,7 @@
 Author: Vladyslav V. Prodan
 Contact: github.com/click0
 Phone: +38(099)6053340
-Version: 2.5.1
+Version: 2.6.0
 License: BSD 3-Clause "New" or "Revised" License
 Year: 2025-2026
 
diff --git a/unmask_data.py b/unmask_data.py
index bb54e4d..c07419c 100644
--- a/unmask_data.py
+++ b/unmask_data.py
@@ -2,18 +2,22 @@
 # -*- coding: utf-8 -*-
 
 """
-Data Unmasking Script v2.5.1
+Data Unmasking Script v2.6.0
 Відновлення оригінальних даних з замаскованого файлу
 
-ОНОВЛЕНО В v2.5.1:
-- Рефакторинг: розбито на пакет unmasking/ (helpers, engine, io, cli)
-- Додано __main__.py: запуск з кореня репо — python . mask / python . unmask
-- Зворотна сумісність: всі імпорти з unmask_data продовжують працювати
+ОНОВЛЕНО В v2.6.0:
+- Відновлення ініціалів (категорія initials у mapping)
+- Повторні текстові дати відновлюються всі (instance tracking)
+- Розпізнавання mapping-файлів усіх версій 2.x (раніше 2.3+ падали у v1-логіку)
+- O(n) заміни замість O(n^2) на великих файлах
+
+Архітектура (з v2.5.0): тонка обгортка над пакетом unmasking/
+(helpers, engine, io, cli); запуск з кореня репо — python . unmask
 
 Author: Vladyslav V. Prodan
 Contact: github.com/click0
 Phone: +38(099)6053340
-Version: 2.5.1
+Version: 2.6.0
 License: BSD 3-Clause "New" or "Revised" License
 Year: 2025-2026
 """
diff --git a/unmasking/__init__.py b/unmasking/__init__.py
index 804e35d..99e65fd 100644
--- a/unmasking/__init__.py
+++ b/unmasking/__init__.py
@@ -4,7 +4,7 @@
 """
 Unmasking package — data restoration from masked files.
 
-Refactored from monolithic unmask_data.py in v2.5.1.
+Refactored from monolithic unmask_data.py (v2.5.0).
 """
 
 from unmasking.cli import __version__, main
diff --git a/unmasking/cli.py b/unmasking/cli.py
index 59c514f..3c96eba 100644
--- a/unmasking/cli.py
+++ b/unmasking/cli.py
@@ -4,7 +4,7 @@
 """
 CLI entry point for data unmasking.
 
-Extracted from unmask_data.py during v2.5.1 refactoring.
+Extracted from unmask_data.py during the package refactoring (v2.5.0).
 """
 
 import json
@@ -58,7 +58,7 @@
 # ============================================================================
 # МЕТАДАНІ
 # ============================================================================
-__version__ = "2.5.7"
+__version__ = "2.6.0"
 
 
 def main():
diff --git a/unmasking/engine.py b/unmasking/engine.py
index b3e35c9..a807666 100644
--- a/unmasking/engine.py
+++ b/unmasking/engine.py
@@ -4,7 +4,7 @@
 """
 Core unmasking logic: text and JSON restoration.
 
-Extracted from unmask_data.py during v2.5.1 refactoring.
+Extracted from unmask_data.py during the package refactoring (v2.5.0).
 """
 
 import re
@@ -141,10 +141,21 @@ def unmask_ranks_gender_aware(masked_text: str, masking_map: Dict) -> Tuple[str,
         else:
             stats["skipped_count"] += 1
 
-    # КРОК 3: ВИКОНАННЯ ЗАМІН (з кінця до початку)
-    replacements_to_do.sort(key=lambda x: x[0], reverse=True)
+    # КРОК 3: ВИКОНАННЯ ЗАМІН
+    # Сегментами в порядку документа — O(n) замість квадратичної
+    # пересборки рядка на кожну заміну
+    replacements_to_do.sort(key=lambda x: x[0])
+    segments = []
+    prev_end = 0
     for start, end, original in replacements_to_do:
-        restored_text = restored_text[:start] + original + restored_text[end:]
+        if start < prev_end:
+            continue
+        segments.append(restored_text[prev_end:start])
+        segments.append(original)
+        prev_end = end
+    if segments:
+        segments.append(restored_text[prev_end:])
+        restored_text = ''.join(segments)
 
     return restored_text, stats
 
@@ -175,12 +186,24 @@ def unmask_other_data(masked_text: str, masking_map: Dict) -> Tuple[str, Dict]:
             else:
                 stats["skipped_count"] += 1
 
-    replacements_to_do.sort(key=lambda x: x[0], reverse=True)
+    # Сегментами в порядку документа — O(n); перевірка відповідності маски
+    # йде по незмінному тексту, перекриття пропускаються
+    replacements_to_do.sort(key=lambda x: x[0])
+    segments = []
+    prev_end = 0
     for start_pos, end_pos, original_value, masked_value in replacements_to_do:
-        if restored_text[start_pos:end_pos].lower() == masked_value.lower():
-            masked_segment = restored_text[start_pos:end_pos]
-            original_value = _apply_original_case(masked_segment, original_value)
-            restored_text = restored_text[:start_pos] + original_value + restored_text[end_pos:]
+        if start_pos < prev_end:
+            continue
+        masked_segment = restored_text[start_pos:end_pos]
+        if masked_segment.lower() != masked_value.lower():
+            continue
+        original_value = _apply_original_case(masked_segment, original_value)
+        segments.append(restored_text[prev_end:start_pos])
+        segments.append(original_value)
+        prev_end = end_pos
+    if segments:
+        segments.append(restored_text[prev_end:])
+        restored_text = ''.join(segments)
 
     return restored_text, stats
 
diff --git a/unmasking/helpers.py b/unmasking/helpers.py
index 39aafcf..e54ab1f 100644
--- a/unmasking/helpers.py
+++ b/unmasking/helpers.py
@@ -4,7 +4,7 @@
 """
 Helper functions for unmasking operations.
 
-Extracted from unmask_data.py during v2.5.1 refactoring.
+Extracted from unmask_data.py during the package refactoring (v2.5.0).
 """
 
 import re
diff --git a/unmasking/io.py b/unmasking/io.py
index 68e8e3e..ca1235a 100644
--- a/unmasking/io.py
+++ b/unmasking/io.py
@@ -4,7 +4,7 @@
 """
 File I/O and validation for unmasking operations.
 
-Extracted from unmask_data.py during v2.5.1 refactoring.
+Extracted from unmask_data.py during the package refactoring (v2.5.0).
 """
 
 import json