Each member employer that has adopted a plan providing retirement benefits under Code Section 47-5-40 is authorized in its plan and contract to determine what credit, if any, shall be allowed for prior service. The financial liability incurred by the member employer for any such prior service credits allowed shall be actuarially determined and incorporated in the contract, which shall set forth the manner in which such liability shall be defrayed by the member employer.
OCGA § 47-5-44