"Third. New States, of convenient size, not exceeding four in number, in addition to said State of Texas, and having sufficient population, may hereafter, by the consent of said State, be formed out of the territory thereof, which shall be entitled to admission under the provisions of the federal constitution. "
(This is Texas trivia for mutual amusement, not a serious suggestion.)
What was annexed and what is now Texas are not the same thing. Some of the area of the original Texas already is part of different states (no other state is a majority of old Texas though)
https://www.tsl.texas.gov/ref/abouttx/annexation/march1845.h...
"Third. New States, of convenient size, not exceeding four in number, in addition to said State of Texas, and having sufficient population, may hereafter, by the consent of said State, be formed out of the territory thereof, which shall be entitled to admission under the provisions of the federal constitution. "
(This is Texas trivia for mutual amusement, not a serious suggestion.)