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In X-Men: DoFP a significant alteration of the timeline is occurred. For a moment let's ignore that alteration. We are in 1973 and Professor X keeps taking his medication for the next few years in order for him to walk -which has the side effect of losing his mental powers. How Xavier ends up in the '80s, when we see him in the beginning of X-Men 3 both walking and also having his mutant powers? Is that a continuity error or is it explained somehow? I know that Singer doesn't like the events of X-Men 3, therefore he acknowledges what happened in that movie in X-Men DoFP (for instance, Cyclops is absent from the future scenes because he was killed in X3).
Note to duplicate report: This question is trying to explain why Professor X is seen walking and having his mental powers at the beginning of X-Men 3 (early '80s), while in X-Men DoFP it is explicitly mentioned that the treatment for his spine has affected his powers. The linked question, though, is trying to explain why Xavier walks in early '80s after being shot from Magneto at the end of X-Men: First Class, ignoring the events of DoFP.