Net business loss carry-forward.

Except as provided in par. (b) and s. 71.80 (25), insurers computing tax under this subchapter may subtract from Wisconsin net income any Wisconsin net business loss incurred in any of the 20 immediately preceding taxable years, if the insurer was subject to taxation under this chapter in the taxable year in which the loss was incurred, to the extent not offset by Wisconsin net business income of any year between the loss year and the taxable year for which an offset is claimed and computed without regard to sub. (2) (a) 8. and 9. and this subsection and limited to the amount of net income, but no loss incurred for a taxable year before taxable year 1987 by a nonprofit service plan of sickness care under ch. 148, or dental care under s. 447.13 may be treated as a net business loss of the successor service insurer under ch. 613 operating by virtue of s. 148.03 or 447.13.