Nope, it's in the DI manual*. They're called initial counters. An FBS school can only bring in 25 student-athletes that are counting against the 85 scholarship limit for the first time. FCS schools can bring in 30 initial counters against the 85 total limit(63 scholies over 85 players). NCAA regs allow greyshirts to be initial counters in either their first academic year or their first playing year, whichever the school prefers. But they must be an initial counter at some point.
Say a recruit enrolled at NDSU for the first time a month ago. If we did not bring in our maximum of 30 initial counters last fall, the recruit could be added to the 2009 initial counter class. If we did bring in 30 initial counters, then he would be added to the 2010 class and we'd have 29 spots left open. That all presupposes that he was receiving a scholarship for the current semester. If he was paying his own way until the fall, then he would have to be counted as part of the 2010 class.
Any school can sign as many kids as they want, but they can only give scholarships to certain numbers and types, and they can only bring a certain number to fall camps.
*Bylaw 15.5.6 and the follow-ups