It seems a lot of these come down to the fact that people don’t do a final sanity check. I have seen it quite a few times where people threw out numbers in meetings that simply didn’t make sense but weren’t challenged.
We've seen this in customer deployments as well [1], that's why we always recommend UIs linked to a spreadsheet that help with verification & correctness of the underlying spreadsheet logic.
[1] Implementations of MintData spreadsheets for internal tooling & line of business applications.
