There are a few mutants who never associated themselves with the X-Men or any of their off-shoots until this decade. Some of those examples include Typhoid Mary, Molly Hayes and Squirrel Girl (whose X-gene has now been retconned). These are the exceptions who I think don't belong to Fox. However, if Marvel wants to use them in a movie or live action show, they cannot acknowledge their mutant heritage. That's how I see it.