(1) Taxpayer s are required to report to the department adjustments or corrections to their taxable income made by the IRS or other competent authority within 90 days after receiving official notice of such change.   If the taxpayer fails to report these adjustments or corrections within 90 days thereafter:

(a) f or tax periods beginning before March 13, 1997, the period within which a deficiency in tax may be assessed extends for five years from the date the changes orcorrections in the taxpayer's federal taxable income become final and are filed with the department.

(b) f or tax periods beginning after March 13, 1997, the period within which a deficiency in tax may be assessed extends for three years from the date the changes or corrections in the taxpayer's federal taxable income become final and are filed with the department.

(2) If a taxpayer files an amended federal income tax return for any year changing or correcting his taxable income and if the taxpayer fails to file a corresponding amended Montana corporation license tax return with the department within 90 days thereafter:

(a) for tax periods beginning after March 13, 1997, the period within which a deficiency in tax may be assessed extends for three years from the date the corresponding amended Montana corporation license tax return is filed; and

(b) for tax periods beginning before March 13, 1997, the period within which a deficiency in tax may be assessed extends for five years from the date the corresponding amended Montana corporation license tax return is filed.