I came across this old drawing which made me smile. Thought it an appropriate follow-up post.
This was sketched sometime around '70, maybe. I don't know who the artist was.
We can tell it's pre-80 because some of the predictions that it makes didn't pan out in history. (Ringo still has all his hair, for one).
On an analogous note, this is also how we know the gospels came shortly after the Jewish War. The predictions that they make about the coming kingdom of God right after the fall of Jerusalem aren't quite what happened in actuality as time rolled on. (I'm talkin' just the pedestrian stuff, never mind the theological accretions!)