You can sign more than 25, as long as you signed less than 25 the previous year. The unused spots are available for early enrollees only, however.
The rules, as I understand them, per the NCAA...the only one's that really count...
"Sign" is a word that has different meanings to different people.
85 on Scholarship max. No more. Medical Scholarships don't count.
25, max, may enroll in the fall on scholarship. No more, whether you're at 85 or not. If you have less than 25 spots to fill the 85, then you can't even enroll 25, only the number to get you to 85...unless...read below.
After that, the math gets really fuzzy, and depends on who is counting, what drugs they are on, what agenda they have, etc. JC Early Enrollees can count back to the previous year, IF there are slots available in the 25. Grayshirts? I have no idea how they count. The NCAA likely doesn't either.
Per NCAA bylaws, you can accept an unlimited number of LOI's on or after NSD, but in the fall only 25 may enroll on football scholarship, max, unless a lesser number puts the total on scholarship at 85. I have no idea how long you have to process players if you exceed 85, but I'm sure there's a grace period to "cut down the roster". Or it may just be that you have to be at 85 total, by the time the fall camp starts. Seems Nick's processing all takes place between NSD and fall camp.
As I understood it, the SEC capped the number of "LOI's" that can be accepted on NSD at 28 a couple of years ago...may have been 25. As far as I can tell, nobody is abiding by either cap number, nor is the SEC holding them to it.
As far as I can tell, only 2 numbers have any real meaning. 25 is the MAXIMUM number of recruits that may enroll in a school year on football scholarship (most times this means in the fall, but can be accounted for by counting JCs that enroll early prior to the next school year cycle if 25 didn't enroll in the fall). And, 85 is the max you may carry on football scholarship, though I don't know when that counts is made. My guess is, that let's just say you had 85 on scholarship in February, all returning, and you got 25 LOI's. You could take in all 25, but by fall camp, or the beginning of the school year, you'd have to process 25 of the returning players by either converting them to medical scholarship, or by not renewing their scholarship for whatever reason.
Saban has figured out the way da Bahr used to do it by stockpiling players either by using loopholes in the rules, or being so knowledgeable of them, he knows how to get around the rules that are in place.