Mo. Rev. Stat. § 169.400

Should any change or error in records result in any member or beneficiary receiving from the retirement system more or less than the person would have been entitled to receive had the records been correct, the board of trustees shall have the power to correct such error and, as far as practicable, may adjust the payments in such a manner that the actuarial equivalent of the benefit to which such member or beneficiary was correctly entitled shall be paid.