According to some googling, Romney wrapped up the 2012 nomination with a Texas primary win. That primary was MAY 20, 2012, not March.
Looks like I was almost 3 months wrong, looks like the Pubbie primary in 2012 was may 29.
http://www.thegreenpapers.com/P12/TX-R
That reinforces my opinion that TX primary is way too late to have any real say in the process.