Earlier today we said we had found nothing for these two. A second search did.
- South Dakota: the Department of Revenue's sales and use tax page says a return is due the 20th of the month after the reporting period, whatever the filing frequency. Electronic payments are due the 25th; the worksheet does not model that split.
- Rhode Island: third-party guides agree monthly returns are due the 20th. They disagree on quarterly dates, so those are not modelled. The state's own site was unreachable from our session.
Both equal the worksheet's default of 20, now listed explicitly so a later change to the default cannot move them. Check your own notice: these are search excerpts, not the forms.