Mo. Rev. Stat. § 104.339: Creditable prior service, members entitled to.

1. Any employee who became a member of the system, on the first day of the first month following the original effective date of sections 104.310 to 104.540, September 1, 1957, shall be given creditable prior service with the state. All such creditable prior service must be established to the satisfaction of the board.

2. Any member of the system employed on or after August 13, 1988, and who served as an employee prior to September 1, 1957, but was not an employee on that date, shall be entitled to the creditable prior service that such employee would have been entitled to had such employee become a member of the retirement system on the date of its inception.