I've said this before, but the individuals in charge of the X franchise have made it clear that they want to create a single continuous universe for the franchise, something that has not yet happened successfully for one reason or another. We know at this point - based on the actual content of both films - that First Class has rendered Origins: Wolverine out-of-continuity (not only due to Xavier having already been paralyzed by the time the events of Origins: Wolverine occur, but also because of Emma Frost's inclusion in FC [there is absolutely no way that she can be an adult in FC and a teenager in Origins: Wolverine]), but, as I have repeatedly said, the continuity status of The Last Stand is still currently in limbo pending the completion of Days of Future Past.