The sales tax return worksheet in AI Bookkeeper lists a due date for each state. Most are the 20th of the month after the period. Michigan is not quite that: Treasury's filing pages put monthly and quarterly returns on the 20th, but annual filers on February 28. The worksheet gave them January 20, a month early. It now returns February 28 for --state MI --freq annual.
Checked in the same pass against search excerpts of state and vendor pages: Wyoming (last day of the month after), Kansas (25th), Oklahoma and Mississippi (20th) match the table. Indiana's 30th could not be confirmed, so it stays as it was and is flagged in the README. The state pages were not fetched in full, so treat the date as a worksheet value and check your own notice. This is not tax advice.