Tell us. We correct it, record the correction in that workbook’s changelog, and give the corrected version free to everyone who bought that tax year — or refund you, if you would rather not continue. That is a limited accuracy warranty in our Terms of Use, not a goodwill gesture. What it does not do is take over your review: it covers our arithmetic against the legislation a workbook cites, not judgment calls, elections or filing positions, and the accuracy of what you file remains yours to establish. We never need your workbook or your client’s figures to check a formula, and we ask you not to send them.