Mo. Rev. Stat. § 86.292

If the board of trustees is unable to refund the accumulated contributions of a member or to commence payment of benefits within five years after such refund or benefits are otherwise first due and payable, the accumulated contributions shall remain assets of the retirement system. If proper application is thereafter made for refund or benefits, the board shall make payment, but no credit shall be allowed for any interest after the date the refund or benefits were first due and payable.