(a) Unless modified under Subchapter J, Chapter 49, Water Code, or other law, the authority's territory is composed of the territory in each county in Texas, other than Fannin County, that is located wholly or partly in the watershed of the Sulphur River and its tributaries with confluences with the Sulphur River upstream from the eastern boundary of Texas, as those watersheds and tributaries are defined by maps on file with the development board.
(b) The boundaries of the authority form a closure. A mistake in the description of the boundaries in the legislative process or another mistake does not affect:
(1) the authority's organization, existence, or validity;
(2) the authority's right to issue any type of bond for a purpose for which the authority is created or to pay the principal of or interest on the bond; or
(3) the legality or operation of the authority or its governing body.