Sec. 8. Postretirement Increase. The monthly benefit payable on and after July 1, 1980, to a member, or a survivor or beneficiary of a member, who retired or was disabled:
(1) before July 2, 1963, shall be increased by nine percent (9%);
(2) after July 1, 1963, and before July 2, 1968, shall be increased by six percent (6%); and
(3) after July 1, 1968, and before July 2, 1973, shall be increased by three percent (3%).
The increase specified in this section shall be based upon the date of the member's initial retirement or disability. This section does not apply to benefits payable in a lump sum. The increases provided by this section are in addition to any other increase provided by law.