The latter two games are essentially higher builds of the original engine. Of course, as time goes on, various engines may have easily passed what the Unreal Engine used to be, but the engine, at heart, is the same one. Of course, it is given that it will be far more powerful than before, but the new build comes off the original, and so, it is still the Unreal Engine.

By the time a game using an older build of the engine is released, it will be overlooked all too quickly. Then again, a game is a game, not that it would ever be made and fully released at all.