Factual error: Young Dewey is seen driving a tractor near the beginning of the movie. The year is supposed to be 1946, but the tractor is a 1950's Ford.
Factual error: When August sits down at the piano in the church and begins to play, he plays a passage of ascending notes (his hand is actually on camera so you see it move to the right, up the piano). However, the audio that you actually hear is a passage of descending notes.
Factual error: In the Pop Goes My Heart video, the keyboard is a Roland D-50. At the start of the video it's said that it was from 1984. The D-50 wasn't released until 1987 to compete with the Yamaha DX7. (00:01:15)
Factual error: The phone at the Peacocks house is too modern for the time - the cord going into the handset had a clip in cord versus being attached directly to the piece.
Factual error: When the Chipmunks are going on tour and all of the cities are listed, it says that they're going to "Phoenix - NV" however it's clear they are in Arizona not Nevada, so it should have said "Phoenix - AZ." (01:02:40)
Factual error: When the girls talk at the beginning of the movie, they can fully hear and understand each other even when they are at massive distance from the webcams they are supposedly using to communicate.
Factual error: At the end of the movie, Pat is watching a news report about John Lennon's death, which is intercut with scenes of Darby making preparations for his fatal overdose. Darby died almost a whole day before Lennon's assassination.