Each employee annuitant who terminated service prior to the effective date of this amendatory Act of 1971 is entitled to receive a monthly incremental retirement annuity, effective January 1, 1972, of .167% of his monthly retirement annuity amount, multiplied by the number of months from the effective date of his annuity to January 1, 1972. This monthly incremental annuity shall be increased on each January 1 thereafter during the lifetime of the annuitant by 2% of the monthly retirement annuity amount. Beginning January 1, 1984 and each January 1 thereafter, the monthly incremental annuity shall be increased by 3% of the monthly retirement annuity amount. The incremental annuity is payable only if the annuitant agrees to pay the fund an amount equal to 1% of 1/12 of his annual final rate of earnings, determined as of the date of his retirement, multiplied by the number of full years of service. The annuitant, prior to December 1, 1971, may authorize the fund to deduct the payment from his annuity if the total payment can be deducted in one month. If the agreement or payment is received by the fund prior to December 1, 1971, the incremental annuity shall be effective January 1, 1972. If the agreement or payment is not received before December 1, 1971, the incremental annuity shall be effective the first day of the next month after receipt of payment by the fund, but if received after the 15th day, the first day of the month following the next month, and shall not be paid retroactively.
     The monthly retirement annuity amount, for the purpose of this Section, shall be the annuity amount initially awarded or, if adjusted under paragraph (b) of Section 7-142, the adjusted amount, disregarding any incremental annuities previously granted.