About screwed up dates:
The ultimate example, for me, is the blue parka scene. At the beginning of the scene, the screenplay states that it is 1969. Then, three lines later, it says that Lureen is sitting in front of a calendar dated 1973.
Lureen may be on top of things, but I've never known anyone to put up a calendar four years early.
(I suspect that the dates at the end of the movie were changed around so that Alma Jr. would be the same age during the "does he love you" scene as Jack and Ennis were when they met. Nice parallel, but nobody seems to have sat down with the screenplay and checked the timeline to see if it made sense.)
(Also, it seems that the movie as filmed is deliberately vague about the precise dates, even though they are stated in the screenplay. Most of the obvious time markers -- the calendar, for instance, or the drive-in showing of
The Empire Strikes Back that was in an early script draft -- aren't in the final movie. And there aren't other obvious time markers, either... no JFK, no astronauts, no Nixon, no bicentennial. Just the vaguest reference to Vietnam ("...if the army don't get me") and to late-70's inflation. Actually, I kind of like it that way... I like the feeling of drifting along without obvious "here we are in 1975!" kinds of references.)