The retirement system shall correct errors and, as far as practicable, shall:
(1) in the case of underpaid benefits, adjust future benefit payments so the actuarial equivalent of the benefit to which the member or benefit recipient is correctly entitled will be paid;
(2) in the case of overpaid contributions, refund the excess contributions;
(3) in the case of unpaid contributions, recover the amounts owed for unpaid contributions; and
(4) in the case of overpaid benefits, recover the amounts owed for overpayment.