The Big Ten allows schools to oversign by three players, but even that rule is drastically different from the NCAA rule now in effect. Schools are allowed three over the 85-man limit, not the annual 25-man limit. There is no limit to the number of scholarships given in a year. The Big Ten does not abide by the NCAA rule because the Big Ten's rule is considered more restrictive.
If, for example, Iowa ends a season with 20 open scholarship spots, then the Hawks may sign 23 players. No more. This year Illinois has 30 commitments. In other words, Illinois has no more than 58 scholarship players (88 minus 30).
If a Big Ten program chooses to oversign, it then must document exactly how it came under the 85-scholarship limit.
I hope I answered your question.