In case any officer whose signature appears on any bonds or whose facsimile signature appears on any coupon ceases to be an officer before the delivery of the bonds, the signature shall nevertheless be valid and sufficient for all purposes the same as if he had remained in office until the delivery. All such bonds shall be signed by the chairman of the authority, and the official seal of the authority shall be affixed thereto and attested by the secretary of the authority; and any coupons attached thereto shall bear the signature or facsimile signature of the chairman of the authority. Any coupon may bear the facsimile signature of such person and any bond may be signed, sealed, and attested on behalf of the authority by such persons as at the actual time of the execution of the bonds shall be duly authorized or hold the proper office, although at the date of the bonds the persons may not have been so authorized or shall not have held such office.