Sec. 6.12. 13TH AND 14TH CHECKS FOR BENEFICIARIES. (a) For any year in which the board authorizes disbursement of a 13th or 14th pension check to retirees under Section 5.11 or 5.12 of this Act, the board shall also authorize disbursement of a 13th or 14th check to each beneficiary entitled to receive an annuity in the last month of the fiscal year preceding the fiscal year in which the check is disbursed.

(b) The amount of the 13th or 14th check is equal to the amount of the annuity payment made in the last month of the preceding fiscal year, except the amount of the check shall be prorated for any beneficiary who has been receiving an annuity for less than one year so that the amount of the check is one-twelfth of the check that would have been paid to the beneficiary receiving an annuity for a full year times the number of full months an annuity has been paid.