When a municipality that is part of an authority annexes territory that before the annexation is not part of the authority, the annexed territory becomes part of the authority.
Tex. Transp. Code § 451.551
ADDITION OF TERRITORY BY MUNICIPAL ANNEXATION
Acts 1995, 74th Leg., ch. 165, Sec. 1, eff
Official source: Texas Constitution and Statutes. Reproduced from public-domain Texas statutes; confirm against the official source for the current text. Not legal advice.