Validating that a complex spreadsheet is correct is notoriously extremely difficult at the best of times; unfortunately they are about the closest thing to a write-only language in common use, and you really have to front load a lot more care than you do in conventional modern languages. The usual safeguards of testing and code review are essentially absent.

I’m sceptical that anyone really _should_ be using generative AI for anything where correctness matters at all, but spreadsheets in particular seem close to a worst-case scenario.