The entire NCAA now follows the SEC 25-man signing rule limit, as well as adhering to the same back counting rule.
There is no hard number for back counting. It depends on what you signed in previous classes along with the kids you are bringing in. Ole Miss and Georgia could both sign 30+ this year if they saw fit because of small signing classes in previous years, while MSU can only sign 25(+ the two we have previously signed that are at Hargrave). You have to look at EEs and total signing over multiple years until the last time you signed over 25 spring enrolees in a single class(it isn't as easy as just looking back at a single season)...