Last year at my Houston interview, Dr. Pierpont said something along the lines that they only accept enough students to potentially fill 1/3 of their class on Decemeber 1st. So that is around 30 or so students. Some of the students that are accepted to Houston on December 1st will also be accepted to other schools on December 1st, and will not choose to go to Houston. Houston to my knowledge is the only school in Texas that doesn't really intend on filling their entire class on December 1st in order to give students who submitted later or took their DAT later a chance to interview and what not. I heard that Baylor filled almost their entire class from December 1st acceptances last year, and San Antonio to my knowledge had majority of their class filled by February. So, I think it was a smart decision on your part to move Houston.
This is not to say that spots don't open up at San Antonio and Baylor at a later date, because they do. Someone might really have their heart set on going to San Antonio and they are holding a spot at Baylor and when they get accepted a spot opens up. It works this way among all three schools.