ANSWER KEY - customer 09 (WRONG copy)
Document: Monthly statement, titled "Statement of Account" (STATEMENT_006)
File: 03_monthly_statement/statement_customer_09_wrong.pdf (4 pages)
Customer: Kavya Chopra   Lender: Ulmarin Finance (fictional)

Error type: MISSING_TRANSACTION - a transaction is missing.
Page: 3 (where the left-out line belongs)
Field: the whole transaction line under "Transaction details": [20 Jul 2025 | Purchase | Chaurahvan Fuel Centre | Kolkata | CONTACTLESS | 1,964.87 | Dr]
Correct value: 1,964.87
Printed value: none - the line is not printed at all

How it can be caught from this customer's documents:
The Purchase line of 1,964.87 dated 20 Jul 2025 is left out (it belongs on page 3). The remaining Purchase lines no longer add up to "Purchases" in the account summary, and the opening balance plus the Dr lines minus the Cr lines no longer equals the closing balance; in both, the gap is exactly the missing line's amount. No other published document of this customer prints 1,964.87 (searched).

Engine record:
  corruption id COR_7C615F9A61; mode ISOLATED (only this element was changed; nothing else was adjusted to match)
  reference detector rules whose finding names this field, with the full observation set (the documents and the event feed): line_feed, statement_category, statement_lines
  ... and reading only this customer's nine published documents: statement_category, statement_lines

Every figure in this pack comes from a simulated ledger; this one was altered on purpose for training and testing.