Should a disability beneficiary be restored to service and should his or her annual earnable compensation then or at any time thereafter be equal to or greater than his or her average final compensation at retirement, or should any other beneficiary be restored to service, his or her retirement allowance shall cease and the beneficiary shall again become a member of the Retirement System. Anything in this chapter to the contrary notwithstanding, upon his or her subsequent retirement he or she shall be credited with all the service creditable to him or her at the time of his or her former retirement. However, if such beneficiary is restored to membership after the attainment of the age of 55 years, his or her pension upon subsequent retirement shall not exceed the sum of the pension that he or she was receiving immediately prior to his or her last restoration to membership and the pension that may have accrued to him or her on account of membership service since his or her last restoration to membership. (Added 1973, No. 251 (Adj. Sess.), § 3.)