Cal. Gov't Code § 20160

(a) Subject to subdivisions (c) and (d), the board may, in its discretion and upon any terms it deems just, correct the errors or omissions of any active or retired member, or any beneficiary of an active or retired member, provided that all of the following facts exist:
1. (1) The request, claim, or demand to correct the error or omission is made by the party seeking correction within a reasonable time after discovery of the right to make the correction, which in no case shall exceed six months after discovery of this right.
2. (2) The error or omission was the result of mistake, inadvertence, surprise, or excusable neglect, as each of those terms is used in Section 473 of the Code of Civil Procedure.
3. (3) The correction will not provide the party seeking correction with a status, right, or obligation not otherwise available under this part.
  Failure by a member or beneficiary to make the inquiry that would be made by a reasonable person in like or similar circumstances does not constitute an “error or omission” correctable under this section.
(b) Subject to subdivisions (c) and (d), the board shall correct all actions taken as a result of errors or omissions of the university, any contracting agency, any state agency or department, or this system.
(c) The duty and power of the board to correct mistakes, as provided in this section, shall terminate upon the expiration of obligations of this system to the party seeking correction of the error or omission, as those obligations are defined by Section 20164.
(d) The party seeking correction of an error or omission pursuant to this section has the burden of presenting documentation or other evidence to the board establishing the right to correction pursuant to subdivisions (a) and (b).
(e) Corrections of errors or omissions pursuant to this section shall be such that the status, rights, and obligations of all parties described in subdivisions (a) and (b) are adjusted to be the same that they would have been if the act that would have been taken, but for the error or omission, was taken at the proper time. However, notwithstanding any of the other provisions of this section, corrections made pursuant to this section shall adjust the status, rights, and obligations of all parties described in subdivisions (a) and (b) as of the time that the correction actually takes place if the board finds any of the following:
1. (1) That the correction cannot be performed in a retroactive manner.
2. (2) That even if the correction can be performed in a retroactive manner, the status, rights, and obligations of all of the parties described in subdivisions (a) and (b) cannot be adjusted to be the same that they would have been if the error or omission had not occurred.
3. (3) That the purposes of this part will not be effectuated if the correction is performed in a retroactive manner.