Wis. Stat. § 79.08
If the department of administration or the department of revenue determines by August 15 of the year following any distribution under this subchapter that there was an overpayment or underpayment made in any certification by the department of revenue or resulting from populations changed as a result of a final court determination or a census determination under s. 16.96(2) (dm) or (e) or in the distribution by the department of administration, the overpayment or underpayment shall be corrected as provided in this section. No corrections to the elements of any distribution may be made after August 15 of the year following the distribution. Any overpayment shall be corrected by reducing the subsequent year's distribution under this subchapter. Any underpayment shall be corrected by increasing the subsequent year's distribution under this subchapter. Corrections shall be made in the distributions to all municipalities and counties affected by the error. Corrections shall be without interest.
Wis. Stat. § 79.08