(a) A member of the Defined Benefit Program who voluntarily requests or agrees to an extension of his or her original term of enlistment, service, or tour of duty shall not receive credit under this part for time served during the extension of military service after December 31, 1958.
(b) In no event shall a member receive credit for more than four years of military service performed after June 30, 1998, except where otherwise authorized in accordance with Chapter 14.5 (commencing with Section 22850).