Set in 1960, but when Bobby is reading the newspaper, he reads about Nixon running for Vice President, which he did in 1952 and 1956. Later, on the radio they played Only You from the Platters, which came out in 1955.
When Brautigan relates the story of Bronko Nagurski's return to football in 1943, he states that the Chicago Bears played the "crosstown Cardinals" (at around 52 mins). Everything about this story is factual except the opposing team was actually the Washington Redskins.
When Harry Doolin and the other boys are bullying Bobby and Carol, Carol's hair clip changes its height from low forehead (at around 6 mins) to mid-cheek (at around 29 mins) (after struggling against one of the boys), up to eyebrow (at around 33 mins), down to low cheek (at around 44 mins) (again struggling), back to eyebrow (at around 3 mins), and down to low cheek (with no struggling).
On the front porch, Bobby's newspaper switches from folded (at around 7 mins), as Bobby stands and holds his fingers in a cross, to unfolded (at around 31 mins), as Bobby sits back down, between shots.
When Ted offers Bobby the job of reading the newspaper to him as they are seated at the table in Ted's apartment, things move about on the table top. At 17:25, in a medium shot of Bobby from behind Ted, the cup, sugar and creamer, and Bobby's root beer are aligned. At 17:26, in a medium shot of Ted drinking his root beer from behind Bobby, the sugar and creamer have moved to Bobby's left out of alignment. At 17:29, in a medium shot of Bobby from behind Ted, the sugar and creamer have moved back, but Bobby's root beer has moved to his left out of alignment.
The shot is flipped at the end of the movie when Bobby is riding his Schwinn bike. The kickstand is on the right side and the chain on the left (at around 1h 35 mins), opposite of where they should be (at 15:32-15:56). Also, note that one can clearly see the name "Schwinn" reversed on the side of the bike in this scene (at around 1h 35 mins).
Towards the end of the movie young Bobby is running to meet his mother as they move away. As she sits in the Rambler waiting for him she listens to a car radio that is not there-only chrome covers where dials should be, and a blank radio front.