Does the extension of time to file the 2020 Michigan Individual Income Tax Return, MI-1040 return until May 17, 2021 also apply to the refund deadline under the four-year statute of limitations for claiming a 2016 Michigan refund?

No. The Michigan Department of Treasury has no authority to administratively change the filing deadline for refunds under Michigan's four-year statute of limitations. To claim a refund arising from a 2016 MI-1040, the taxpayer must claim a refund within 4 years after the date set for the filing of the original return (April 15, 2021). Taxpayers who received an extension to file a 2016 return must claim a refund within 4 years after the date the original return was filed under an extension.