(a)
Except as provided in subdivision (b) no refund shall be approved by the board after three years from the 15th day of the calendar month following the close of the period for which the overpayment was made, or, with respect to determinations made under Article 2 (commencing with Section 32271), Article 3 (commencing with Section 32291), or Article 5 (commencing with Section 32311) of Chapter 6 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 pursuant to Section 32273.
(b)
A refund may be approved by the board for any period for which a waiver is given under Section 32273, if a claim therefor is filed with the board before the expiration of the period agreed upon.
(c)
Every claim for refund or credit shall be in writing and shall state the specific grounds upon which the claim is founded.