Sec. 13. (a) The pension portion (plus postretirement increases to the pension portion), provided by employer contributions, of the monthly benefit payable after June 30, 1984, to a member, or a survivor or beneficiary of a member, who retired or was disabled:
(1) before July 2, 1966, shall be increased by four percent (4%);
(2) after July 1, 1966, and before July 2, 1971, shall be increased by three percent (3%); and
(3) after July 1, 1971, and before July 2, 1981, shall be increased by two percent (2%).
(b) The increases specified in this section:
(1) shall be based upon the date of the member's initial retirement or disability;
(2) do not apply to benefits payable in a lump sum; and
(3) are in addition to any other increase provided by law.