[CyclopsWasRight]

Wobbly makes good points about how the Sentinels haven't been in the OT so if they're developed in the 70's where were they.

My theory is someone travelled back and changed events pre-First Class, that led to some differences like Magneto not helping Charles build Cerebro, Charles getting crippled earlier ect..

And most importantly Trask developed Sentinels. This latter didn't effect the OT as that occured before the timeline was changed.

So basically Timeline 1 is X1 - XMO:W. Timeline 2 is First Class onwards, including the future and past of DOFP