The commission in the ordinance or resolution authorizing the bonds may provide for issuance of 1 or more series of additional bonds to complete the project for which the bonds are issued or to make improvements or additions thereto under the terms and conditions as shall be prescribed in the ordinance or resolution authorizing the bonds, one of which shall be a requirement of a sufficient increase in the cash rentals required to be paid under the contract of lease to permit payment of the principal and interest on the additional bonds. The additional bonds when sold and delivered shall have equal standing with those issued in the first instance. The provisions of this act providing for annual installments and the amount thereof and the due date of the first installment for serial bonds shall not be controlling as to additional series of bonds. The bonds issued in the original instance, any additional bonds of equal standing then outstanding, and the proposed additional bonds shall be treated as a single issue for purposes of complying with the requirements of this act for the due date of the first installment and for annual installments with respect to serial bonds.