Multi-currency — Each record converts at its own date

The rate applied to a record is the latest one effective on or before that record was created — never today's rate applied across the whole total. A deal struck at €5,000 in March keeps reporting the same dollar figure in November instead of drifting with the market while nobody touches it. That is how transaction-date conversion works in accounting, and it is what makes a converted figure a historical fact rather than a live market read. Nothing is stamped onto the record. The rate is derived from the record's own creation date against the rates you have declared, which has a consequence worth stating plainly: correcting a rate re-states the conversions that depended on it. That is the right behaviour — you corrected it — and it happens in one visible place rather than being frozen invisibly into thousands of rows.