Minn. Stat. § 270C.62

For purposes of taxes, the term "date of assessment" means the date a liability reported on a return was entered into the records of the commissioner or the date a return should have been filed, whichever is later; or, in the case of taxes assessed by the commissioner, "date of assessment" means the date of the order assessing taxes or date of the return made by the commissioner; or, in the case of an amended return filed by the taxpayer, the assessment date is the date additional liability reported on the return, if any, was entered into the records of the commissioner; or, in the case of a consent agreement signed by the taxpayer under section 270C.33, subdivision 9 , the assessment date is the notice date shown on the agreement; or, in the case of a check from a taxpayer that is dishonored and results in an erroneous refund being given to the taxpayer, remittance of the check is deemed to be an assessment and the "date of assessment" is the date the check was received by the commissioner.