(a) Except as agreed to by the board, no refund shall be approved by the board after three years from the date the payment was due for which the overpayment was made, or with respect to deficiency or jeopardy determinations, after six months from the date the determinations become final, or after six months from the date of overpayment, whichever period expires later, unless a claim therefor is filed with the board within that period. No credit shall be approved by the board after the expiration of that period, unless a claim for credit is filed with the board within that period or unless the credit relates to a period for which a waiver is given by the board.
(b) A refund may be approved by the board for any period agreed to by the board for good cause if a claim for the referral is filed with the board before the expiration of the period agreed upon.