If notice of assessment is given within 6 years after a return was filed and if on that return the taxpayer reported for taxation, or the taxpayers jointly reported for taxation, less than 75 percent of the net income properly assessable, except that no assessment of additional income may be made under this subsection for any year beyond the period specified in sub. (2) unless the aggregate of the taxes on the additional income of such year is in excess of $100 in the case of a return other than a joint return or $200 in the case of a joint return.

If notice of assessment or refund is given to the taxpayer within 180 days of the date on which the department receives a report from the taxpayer under s. 71.76 or within such other period specified in a written agreement entered into prior to the expiration of such 180 days by the taxpayer and the department. If the taxpayer does not report to the department as required under s. 71.76, the department may make an assessment against the taxpayer or refund to the taxpayer within 4 years after discovery by the department.

When an election is made under s. 71.745 (9), with respect to assessments of a tax or an assessment to recover all or part of any tax credit under this chapter in any calendar year or corresponding fiscal year, if notice of assessment is given to pass-through members within one year from the date of the election.