Factual error: The opening scene shows Donna graduating from New College in 1979. That is not possible, women were only first admitted in 1979.
Factual error: Towards the end of the movie when Ally is in her hallway looking at Jack's old concert tour posters hanging on the wall, the poster closest to the camera says "Washington State Fair" and a 2011 date. Unfortunately, that fair did not get that name until 2013. Before that, it was called "The Puyallup Fair" (officially named the "Western Washington Fair"). Locals still call it "The Puyallup Fair" to this day.
Factual error: When Mary and the children go to the bank the long shot of the bank shows a statue that was not erected until 1994.
Factual error: When Buster joins the card game in the saloon, he looks at the hand of the player that had just left. Given the circumstances in the saloon, the cards cannot be spot clean and white as fresh snow. Also, they seem to be plastic cards, which did not exist yet back then.