See, angels can be wibbly-wobbly timey-wimey to a certain extent. (As created beings, their timeline is finite, just as ours is, but this is SPN so *handwave*.)

As far as the Winchester thing goes . . . I happily put on my DW blinders that say certain events in history are fixed, and nothing anyone can do will change them. Like John buying the Impala. Dean (our Dean) wasn't around the first time it happened, because he hadn't been born yet, but it still happened. Unless his in a loop of some sort, and . . .

My head hurts.

Now, when you get to heaven and Ash has a practical use for string theory, then we might get some answers. But until Ash starts holding classes in his roadhouse, I'm just not gonna think about it too hard.