All refunding bonds or notes authorized to be issued under this subchapter and the records relating to their issuance, including any proceedings relating to the redemption of any outstanding bonds or notes, shall be submitted to the attorney general for examination, and if he finds that they have been issued in accordance with law, he shall approve them, and then they shall be registered by the comptroller of public accounts, and after such approval and registration they shall be incontestable. When any such refunding bonds or notes are issued to be exchanged for any outstanding bonds or notes, the comptroller of public accounts shall register and deliver such refunding bonds on surrender for cancellation of the bonds or notes being refunded. When any such refunding bonds or notes are sold, with the proceeds to be used for redeeming any outstanding bonds or notes, the comptroller of public accounts shall register such refunding bonds or notes, even though the bonds or notes to be redeemed shall not have been surrendered for redemption or cancellation.