This is my impression of things:
originally there was weapon x with wolvie, sabertooth, maverick, wraith silver fox, and wildchild I think.
Then somewhere there was deadpool and kane.
During morrisons run on x-men he sorta retconned it and called it weapon plus (wolvie was weapon 10, 10 in roman letters is X) where fantomex (weapon XIII), (probably) stepford cuckoos (weapon XIV), people named weapon XII (Huntsman), weapon XV (ultimaton).
There's also a new weapon x wichmainly consisted of criminals (others coersted) with power-boosts. The line-up included agent x (maverick), sauron, mesmero, marrow, kane, aurora, sabretooth, wildchild, madison jeffries, washout.
Phuh! Now I'm sleepy...