You missed the point of this story. This was in the very, very early days of vaccinations in Harris County. There was hardly any system. Harris County Public Health had to toss their first vaccination registration system, when it turned out signup invitation links could be shared and hundreds of invalid people showed up for appointments.[0] You can be sure this didn't happen after January 1, and protocols for handling extra doses are now very well known.
[0] https://www.houstonchronicle.com/news/houston-texas/houston/...