The proceeds of revenue bonds issued under this article shall be used solely for the payment of the cost of the project or combined project and shall be disbursed upon requisition or order of the chairman of the authority under such restrictions, if any, as the resolution authorizing the issuance of the bonds or the trust indenture mentioned in Code Section 20-3-164 may provide. If the proceeds of such bonds, by error of calculation or otherwise, shall be less than the cost of the project or combined project, unless otherwise provided in the resolution authorizing the issuance of the bonds or in the trust indenture, additional bonds may in like manner be issued to cover the amount of such deficit. Unless otherwise provided in the resolution authorizing the issuance of the bonds or in the trust indenture, such additional bonds shall be deemed to be of the same issue and shall be entitled to payment from the same fund, without preference or priority, as the bonds first issued for the same purpose. If the proceeds of the bonds of any issue shall exceed the amount required for the purpose for which such bonds are issued, the surplus shall be paid into the fund provided in Code Section 20-3-166 for the payment of principal and interest of such bonds.