Sec. 453.306.  INCONTESTABILITY.  Bonds are incontestable after they are:
(1)  approved by the attorney general;
(2)  registered by the comptroller;  and
(3)  sold and delivered to the purchaser.
Acts 1995, 74th Leg., ch. 165, Sec. 1, eff. Sept. 1, 1995.