On the train John wears a white shirt with a black tie. When they run from the train to the waiting car, John is shown inside the car wearing a black turtleneck shirt; this shot was taken from actual footage of the band being mobbed.
When The Beatles leave their fan letters to go clubbing, George and John are wearing white dress shirts covered by coats. When they are seen dancing at the club later, they're wearing black turtlenecks.
Ringo asks the boy why he isn't in school, but it is established that the time is at least 5.50pm. Incidentally, the clock in the canteen has obviously had its hands fixed at 5.50 for continuity reasons, though the second hand is seen going around.
The secretary's legs are uncrossed/crossed as she sits on the edge of her boss' desk.
A Black girl in the audience changes from orchestra to balcony seats between shots.
The closing credits say that all the songs were written by Lennon and McCartney--but the soundtrack includes "Don't Bother Me," written by George Harrison.
When Paul's grandfather is below the stage forging the signatures on the photos, you see the original photo for a second. The signatures on it do not resemble the Beatles' actual signatures at all and look as though they were written by the same person.
Deryck Guyler is credited as being a "Police Inspector" when it's clear from his uniform (and, indeed, how the other officers address him), that he's actually a Desk Sergeant.
Just before the group performs "I Should Have Known Better," John is sitting in the livestock carriage playing with a deck of cards. The sound of shuffling can be heard a moment before he begins to shuffle them. The sound editors did this on purpose to add a surreal element right before the boys' instruments suddenly appear.
While Ringo and the young boy walk along the riverside, Ringo visibly mouths the boy's lines before the boy does.
During "If I Fell," George leans against his amp and knocks it off its stand.
After The Beatles escape the press conference, they find Paul's grandfather and Norm finishing off sandwiches and drinks. George pulls a pen out of his pocket moments before Grandfather says, "Hey, George, give us your John Henry on this picture?"
During the performance of "She Loves You," a man in a light-colored outfit can be seen running through shot on two of the cameras views as seen in the monitors (John can be glimpsed being momentarily distracted by him). No reference is made to this major error, not even by the director who otherwise is shown reacting in shock when Paul's grandfather appears on stage.
When Ringo goes off by himself and buys a dry sandwich in a pub, the barmaid tells him it costs "two and nine" (2 shillings, 9 pence). However, the subtitles (in the HBO edition at least) say "£2.09", apparently misunderstanding the way prices were said in the pre-decimalization era. The "two and nine" price works out to be about £5 in today's terms--a lot, considering the sandwich's quality, but not as outrageous as £2 in 1964, which would have been over £32 in 2022.
When Paul's grandfather and Ringo are sitting in the canteen, the sugar shaker on their table has about two-thirds of sugar in it. Later, when Paul's grandfather picks it up to put sugar in his coffee, it's empty.
When John goes up the stairs after talking to the actress and he says "She looks more like him than I do," the line is obviously dubbed; his mouth isn't moving.
During the beginning of the opera scene, the male opera singer's lip movements do not match the singing.
In the dance scene, Shake visibly mouths "All my loving" while what is heard is "Remember I'll always be true."
At the beginning of the "If I Fell" sequence, John's acoustic guitar can be heard while he visibly stops playing for a brief moment.
The final concert contains three songs ("If I Fell", "I Should Have Known Better", and "She Loves You") for which John played acoustic guitar on rhythm. However, he plays his electric guitar throughout the concert.
Around 00:00:54, a cameraman is reflected on the window when John Lennon is approaching.
During "Tell Me Why", Richard Lester, the movie's director, is seen walking back and forth between the Beatles' and the studio's TV cameras.
Reflected in one of the train windows as the fans chase the group along the station platform in the opening scene.
In the train carriage, just before "I Should Have Known Better," a mic can be seen in the corner when John says "Cor, it's the girls!"
On the train, Shake is shown reading "Son of Mad," but he'd have much difficulty reading it the way he's holding it: the text in this and most of the early Mad books was printed sideways.
During the "If I Fell" and "I Should Have Known Better" numbers, the director's assistant is wildly adjusting the brightness and contrast controls on a camera monitor. Only engineers would be allowed to make those adjustments, and never during a live production.
The "Disagreeable Gentleman" enters the boys' train compartment and makes a pest of himself despite a "Reserved" sign clearly placed on the compartment's window.
The director is not wearing his intercom headphones during the "Tell Me Why" number. Headphones are required during a production to allow the director to communicate with the camera operators and other crew members.