We still see SST packs where the spreadsheet total and the draft portal return differ by a rounding story nobody wrote down. Exempt supplies sit in a tab that was not rolled forward. A credit note issued after cut-off is missing from both.
Before the period is filed, print or export the draft return and sit it next to the working papers. If a line cannot be pointed to a source list, it is not ready. That exercise is an application review, not a redesign of the tax function.
Keep the file. Portal queries arrive months later. The person who clicked submit may have left. The papers should still explain the application.