Talking with a friend who used to coach and now officiates and still currently teaches he brought up two points.
1. Sometimes a schools BEDs documents will include students that the two state associations would not count in their totals, he brought up level 3 special ed kids. I'm not sure if this is still the case or not, but that could impact the final totals.
2. Even though we probably have a good idea of what a schools FRL number is going to be it can vary from year to year more than one might think. He mentioned how some administrators do a really good job of making sure everyone who qualifies for it are signed up, and some simply don't.