(sorry for my english)
Bryan Singer does not explain to the public the resurrection of Professor X (everyone has not seen the scene post-generic X3 + listened the audio commentary). Neither the return of adamantium claws (I know... Magneto). I think this is not an oversight or error. I think it is voluntary.
Last year , the viral campaign showed a timeline where the Sentinels were deployed since 1973 , with internment camps for mutants since 2001, with Magneto involved in the Kennedy assassination , etc ... It does not fit with the trilogy. Not to mention an inconsistency in the film : Logan and Stryker do not know (but in Origins, they met during the Vietnam War) .
Origins are not in continuity ? False. There are images of the film in DoFP : the scene where Victor Creed breaks Logan's claws . So how to fix this ? With a third timeline.
Timeline A (Trilogy) = X1 , X2 , X3, Origins , FC , The Wolverine . Someone (Apocalypse ?) modifies the timeline. There is a breaking point, this is the death of Azazel , Tempest , Angel , which initiates the crusade Mystique . So we switched to...
Timeline B (Apocalyptic) = The apocalyptic future . There are constants (the death of Jean, the loss of bone claws facing Victor) . But Xavier is not dead (so no need for explanations) . Wolverine and has not lost his adamantium claws (same thing) . Wolverine is sent in the past . It then switches to ...
Timeline C (Happy Ending) : Wolverine alter the past and save the future.
This explains absolutely everything!