Mo. Rev. Stat. § 104.200
Should any error in any records result in any member or beneficiary receiving more or less than he or she would have been entitled to receive had the records been correct, the board shall correct such error, and, as far as practicable, make future payments in such a manner that the actuarial equivalent of the benefit to which such member or beneficiary was entitled shall be paid, and to this end may recover any overpayments. In all cases in which such error has been made, no such error shall be corrected unless the system discovers or is notified of such error within ten years after the member's annuity starting date or the date of error, whichever occurs later. In cases of fraud, any error discovered shall be corrected without concern for the amount of time that has passed.
§ 104.200, RSMo