Now we know why Deadpool knows about the X-Men - Logan related
"Logan" (2017) establishes the X-Men as superheroes popular enough in the world to inspire a fictional comic book.
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The X-Men timeline was altered 2 times, not just one (DOFP).
FIRST CLASS was already a "divergence".
Everything is explained here:
THE X-MEN CINEMATIC TIMELINES
http://x-continuity.blogspot.com