Read the last number in a table, used the next one, and created a duplicate

Spreadsheets

Situation: Several people or jobs add rows to the same tracking table, each row with a running number.
What the AI did: It read the last number in the table by eye and used the next one. Another job was adding a row at the same time, and two rows ended up with the same number.
How to ask next time (the operator's example): "Re-read the table right before assigning a number and check that no row already has it. After assigning, count duplicates too."
One question to ask: Is the table re-read right before a number is assigned?
Check it yourself: In a spreadsheet, a helper column with =COUNTIF(A:A,A2)>1 shows TRUE next to any repeated ID. Sort or filter on it after each batch of new rows.
AI used (month): Claude Code (2026-09)
Times this mistake was recorded: once
Source: The operator's work records (the details were changed to a different task)