First, ND is nowhere near being over the scholarship limit, at least for 2021. They're allowed 110 next year. After that, they have plenty of time to manage the roster. If you mean the 25 man limit for the 2020 class, they're nowhere near that either, due to so many early enrollees.
Second, where did you get that he signed in December? It was well publicized that he was waiting to sign in February. It's not like a silent commit. If he had signed a LOI, I think it would have been strange if it wasn't reported by ND.