(a) Except as provided in AS 43.05.260(c), the amount of a tax imposed by this chapter must be assessed within six years after the return was filed.

(b) A decision of a regulatory agency, court, or other body with authority to resolve disputes that results in a retroactive change to a lease expenditure, to an adjustment to a lease expenditure, to costs of transportation, to sale price, to prevailing value, or to consideration of quality differentials relating to the commingling of oils has a corresponding effect, either an increase or decrease, as applicable, on the production tax value of oil or gas or the amount or availability of a tax credit as determined under this chapter. For purposes of this section, a change to a lease expenditure includes a change in the categorization of a lease expenditure as a qualified capital expenditure or as not a qualified capital expenditure. The producer shall

(1) within 60 days after the change, notify the department in writing; and

(2) within 120 days after the change, file amended returns covering all periods affected by the change, unless the department agrees otherwise or a stay is in place that affects the filing or payment, regardless of the pendency of appeals of the decision.

(c) If an alteration in or modification of a producer's federal income tax return or a recomputation of the producer's federal income tax or determination of deficiency occurs that affects the amount of a tax imposed on the producer under this chapter, the producer shall

(1) within 60 days after the final determination of the alteration, modification, recomputation, or deficiency, notify the department in writing; and

(2) within 120 days after the final determination of the alteration, modification, recomputation, or deficiency, file amended returns covering all affected periods.

(d) In this section,

(1) “qualified capital expenditure” has the meaning given in AS 43.55.023;

(2) “return” includes a report, a statement, and an amended return, report, or statement.