Accidentally Deleted Transaction

If I accidentally delete a transaction from the transaction tab (and can’t undo), will it re-appear next time Tiller downloads transactions?

No, a transaction only gets downloaded/filled once per linked spreadsheet. You could use File > Version history to get it back.

Thanks, Mark, for the info. One follow up. How does Tiller determine what’s been downloaded already?

Tiller writes a watermark in the spreadsheet’s developer metadata to keep track.
Tiller does not look at any of the user data in the spreadsheet, including Tiller downloaded data.