Cal. Rev. & Tax. Code § 30266

The board may decrease or increase the amount of the determination before it becomes final, but may increase the amount of the determination only if a claim for increase is asserted by the board at or before the hearing. Unless the 25 percent penalty imposed by Section 30205 or 30224 applies to the amount of the determination as originally made or as increased, the claim for increase shall be asserted within eight years after the date the return for the period for which the increase is asserted is due.