Owwwch. I'm just "fixing" the inconsistencies and the errors. Hopefully there's no American law to prevent me to do that.
Thank you for the delucidations anyway.
P.s.: They can be considered X-Men "retroactively".
I agree with you, Supperhero. After all, the name of the movie was: X-men: First Class. Whether the characters gave themselves that official label is irrelevant; the principles they stood behind were the same as the X-men of the future, and Charles Xavier led the team. Sounds like the First Class of X-men to me.
For myself, I don't really care if the movies and comic books line up exactly--they never do. If that were the case, my favorite, Rogue, would be flying and lifting trucks over her head by now. Oh, well.