I was arguing that point the other day. I see no way a school can enforce a mandate to not sign early.
That would be stupid.
The student could conceivably lose his spot.
STA is a private school. They can do what they want. That’s the bad side of playing for a private as opposed to a public
They absolutely cannot stop these kids from signing anything they want, whenever they want to sign it. An LOI is completely beyond the school's purview. What the schools can control is the early enrollment process as they may not allow the students to take additional courses/credits to graduate early, etc.
Entirely hypothetical with no knowledge behind it, but if a kid is on an athletic scholarship to STA, I could see them putting requirements like this in the application or grant materials. You want to play here and go here for free/heavily subsidized, then you have to sign on signing day to reinforce the marketing part of our athletic programs.