Continuity mistake: Toward the end where the guitarist comes to talk to the kid at his house. He turns the chair around to sit in it backwards, but throws the shirt down onto the ground. When he sits down the shirt is back on the chair.
Factual error: The airplane that Penny Lane is on has small vertical stabilizers on the wingtips, which were not designed into commercial jets until the early 90's.
Continuity mistake: When Russell and William are walking together to "find something real" the VW bus containing the "real Topeka people" drives by behind them 2 times over their left shoulder before pulling up to them a third time on the right side.
Factual error: This is a wardrobe error... in the next morning scene after William has been deflowered, he is still in his Fruit of the Looms, which have the name printed on the elastic waistband. Fruit of the Loom did not print their name on waistbands like this until the 90s, in the 70s they just had single blue and yellow stripes.
Continuity mistake: In the scene where William is sitting in the tub working on his notes, after Penny comes in and sits on the toilet, he scrambles out of the tub and most of the notes which were on the side of the tub fall on the floor. In the next cut when the camera is positioned near the bathroom door, looking in, all of the notes are back on the side of the tub and none are on the floor.
Other mistake: Penny Lane picks up William to go see Stillwater at the Riot Club in L.A. In the very beginning of the scene in her car, a reflection passes up the windshield over William's face as they are driving. The Reflection is the prism and spectrum from Pink Floyd's "Dark Side of the Moon" album. There are no other reflections in this scene.
Continuity mistake: In the scene where William first meets the Bandaids, Black Sabbath comes around in a limo and a couple of the Bandaids touch the windows while they drive around to go down the ramp. Then another shot shows the Bandaids look at the car go around them again.
Factual error: In the radio station scene, the closeup of the turntable tonearm shows a P mount head-shell and Stanton 500 cartridge. Neither was available until the mid 1980s.
Other mistake: When Russell Hammond goes to William's house he spots a professional photo of William and his sister Anita. The photo shows William as a 15 year old with his sister. But Anita has been away working as a stewardess, and has not seen William since he was 11 - who was played by a younger and different actor in those scenes.
Audio problem: When the band is in the limo coming into NYC, Jimmy Fallon gives the band a quick pep talk (e.g., "all you can do is be yourself and leave a pint of blood on the stage"). When the shot changes from inside the limo to outside the limo, the audio does not match the movements of Jimmy Fallon's mouth.
Continuity mistake: In the scene where the man jumps off the roof into the pool, you can see that two people from the top left corner jump into the water to save him; then in the next shot you can see that no one has jumped in because the surface of the water is undisturbed and then the same people jump in again.
Factual error: When William runs into the street to look for Penny Lane, he runs between a row of taxi cabs. Across the street is a blue mid 90's model GMC Suburban. Since the scene takes place in 1973, this is obviously a mistake. It may be necessary to use zoom, depending on the size of your screen.
Continuity mistake: Backstage at the first concert, William is sitting alone writing when Penny comes to talk to him. She has her glasses in her hand as she frames his face to guess his age. As the scene is shown from different angles, she is shown both with the glasses in her hand and without them in her hand depending on the shot.
Continuity mistake: After Russell gets William into his first concert, his rectangular backstage pass is pasted to his left shoulder. Penny Lane shows up with a round backstage pass, and by the time the camera's back on William, the shoulder pass has disappeared.
Factual error: In a party scene, the song "Burn" by Deep Purple is heard. This tune is sung by David Coverdale on the "Burn" album which was recorded in November 1973 and was published in the beginning of 1974, so it can't have been played in 1973.
Continuity mistake: During the scene when the entire group are singing 'Tiny Dancer' on the bus, William cuts Penny off just as she opens her mouth to sing the next line, however the audio of everybody else singing doesn't start that line for another 3-4 beats after Penny opened her mouth.
Continuity mistake: In the scene where Russell and Jeff are arguing about the band's T-shirt their manager is standing behind Jeff, but when Jeff says that Russell " allowed Dick to manage us" Dick is sitting on the couch. At the end of the fight, the manager is standing behind Jeff again.
Factual error: When the band is heading to New York City, there is a scene of them driving over a bridge heading into New York. In the background, you can very clearly see the Citicorp Centre Building. While the movie takes place in 1973, Citicorp Centre was not built until 1978.
Plot hole: In the scene when Russell comes to William's house, thinking it is Penny's, confusion ensues as he begins to question where he is. William's sister, Anita, stands there equally confused as she gazes at Russell, looking as if any random person came to the house, showing no signs (neither speechless shock nor excitement) of recognizing the now famous rock star. Her reaction is completely inconsistent with her character given her fervent love for rock 'n roll. Indeed, not only did she serve as the sole catalyst for William's passion for rock 'n roll but she left home earlier in the film because their mother forbade her listening to it. Moreover, she'd just flown home with William following William's long tour with Russell and Stillwater. Thus, there is no credible possibility that she would not recognize Russell, making her reaction wholly inconsistent with her character.