How does “The headline is the return” work on the HMRC Dues page?

Every headline figure — the tiles, each cell of the grid, the totals — is per the returns filed: owed on filed returns less paid, minus refunds due less received. Once a return is filed the liability is set; HMRC is paid as the return says, and Xero is matched to it afterwards. Xero's estimate for returns not yet filed, and the difference between Xero and the filed figure, are sub-lines that drive the reconciliation — they never drive the payment. A figure the page could not read is shown as unknown with the reason; it is never shown as zero, because a zero would be a claim about the data. Where: HMRC Dues (/accounts/hmrc-dues).