Of course it is. Emma Frost and Banshee are late teen/young adults and Xavier is walking in the mid-eighties in 'Wolverine', yet we know Emma's in her thirties, Banshee's a teen/young adult and Xavier [Blackout]is paralyzed[/Blackout] in 1962 in 'First Class'.
People can argue that those two characters aren't really Emma and Banshee in 'Wolverine', but they clearly are. Some can argue that in a future movie, [Blackout]Xavier regains the use of his legs, and is again paralyzed later on...[/Blackout] but that would severely cheapen the ending if 'First Class'.
The details that are blacked out are also the major contradictions in 'The Last Stand'. [Blackout]In 1962 ('First Class',) Xavier is paralyzed and has his falling out with Magneto. So, why then, in the eighties, would he be seen walking with his friend Erik to meet a young Jean? 'First Class' actually destroys the Dark Phoenix subplot of 'The Last Stand' - by watching the film, we're to assume that Magneto knows how powerful Jean is because he was Xavier's colleague when he met her. If Magneto never saw her true potential as a child, he'd have never have tried to manipulate her into a weapon. It's not just a small continuity error when it comes to the third movie.[/Blackout]
And I'm fine by this... I didn't like 'Wolverine' or 'The Last Stand.'