Mich. Comp. Laws § 38.41

Sec. 41. Should any change or error in the records result in any member, retirant or beneficiary receiving from the retirement system more or less than he would have been entitled to receive had the records been correct, the retirement board shall correct such error and, as far as practicable, shall adjust the payment in such a manner that the actuarial equivalent of the benefit to which such member, retirant or beneficiary was correctly entitled shall be paid.