All bonds issued under this subchapter shall be submitted to the attorney general for examination. If he finds that the bonds have been authorized in accordance with law, he shall approve them, and thereupon they shall be registered by the comptroller of public accounts. After the approval and registration the bonds are incontestable for any reason and are valid and binding obligations in accordance with their terms for all purposes. If the bonds recite that they are secured partially or otherwise by a pledge of the proceeds of a contract or lease made between the board and another party or parties, public agencies, or otherwise, a copy of the contract or lease and of the proceedings authorizing it may or may not be submitted to the attorney general along with the bond records. If submitted, then the approval by the attorney general of the bonds shall constitute an approval of the contract or lease, and thereafter the contract or lease shall be incontestable.