The ethereal glow effect on Joel Grey's Ghost of Christmas Past seems to turn on and off arbitrarily.
While visiting Bob Cratchit's family home, Scrooge and the Ghost of Christmas Present approach the front door but are then seen entering the kitchen area from a side stairway. Bob and Tiny Tim come through the same door a couple of minutes later and enter directly into the kitchen area.
There is no entry in an 1843 Register of Death that would require the signature of Ebenezer Scrooge. There is no space for a witness or next of kin and all information would have been entered by a registrar or clergyman making the opening scene factually inaccurate. In truth, Stewart, who was merely following the opening lines of the original book, was not to blame for this. The fault lies with Charles Dickens who wrote 'The register of his burial was signed by the clerk, the undertaker and the chief mourner' and this may be traced to lack of knowledge on behalf of the author who, aside from signing his own marriage register (a much more detailed pro forma) would have not have come into contact with the registers which were normally kept locked away in the parish chest.
In the snow scenes outside Scrooge's old school, swifts are heard but these migratory birds arrive in May and leave in August.
Twice Scrooge hears Marley's ghost open and close doors in the house before he enters the bedroom. Ghosts do not need to open and close doors to come and go, and in fact, Marley's ghost walks through Scrooge's bedroom door during his entrance.
During the dancing at Fezziwig's, the supposed brick floor can be seen bouncing slightly beneath the footfalls of the dancers, revealing it to be a false flooring.
When the Ghost of Christmas Past is talking to Scrooge near the end of their visit to Fezziwig's, the glow effect for the ghost has been layered over the railing the ghost leans on as well as the ghost himself so that a portion of the rail (matching the ghost's silhouette) glows as well.
When the Ghost of Christmas Past takes Scrooge to Fezziwig's, Scrooge enters by opening the door and walking through. Scrooge and the ghost are not supposed to be able to affect their surroundings, meaning Scrooge shouldn't have been able to open the door. And, Scrooge should not have needed to do so, as he is seen otherwise walking through solid walls to access buildings.
When Scrooge is back visiting his apprenticeship Christmas party, a sideways view of the musician playing the large serpentine wind instrument shows a large black mouthpiece hovering in front of his mouth, whereas moments earlier, from the front, it was a real gray trumpet-like mouthpiece actually attached to the instrument.
When Scrooge is with the ghosts, they walk through walls but over and on the furniture.
At the end of Scrooge's visit to the Cratchit's during Christmas Present, Tiny Tim starts singing "Silent Night" which is then taken up by others in various scenes. Originally a German-language hymn written in Austria, it was not translated into English until 1863, a full 20 years after Dickens wrote "A Christmas Carol".
Marley died in 1836, and the story takes place seven Christmas Eves later in 1843. The caroler at Scrooge's door sings Good King Wenceslas, but the lyrics for that song were not written until 1853.
While Scrooge and the Ghost of Christmas Past are visiting Fezziwig's old shop, Mrs. Fezziwig tells Mr. Fezziwig to "hold your horses." The first documented use of the idiom to "hold your horses," meaning to exhibit patience, was in America in 1843. The "present" sections of this story take place in 1843, in England, putting the Fezziwig scene several decades prior, and on the other side of the world, from when and where the phrase would first come into use.
When the Ghost of Christmas Present walks through Fred's piano, it strikes a discordant sound. The spirits are not supposed to be able to affect the real world.
The name of Scrooge's little sister was "Fan," a popular girl's name in the U.K. and other parts of Europe, more frequently lengthened to "Fannie," not "Fran," as it is pronounced in this movie. One would think Stewart would've known better, owing to his familiarity of the book.
Stewart occasionally forgets to walk like the decrepit old miser that Scrooge was, and instead moves with the gait of a young man.
Scrooge's sister is called "Fran" in this film but called "Fan" (short for "Fannie") in the book. This may be an error but as the film was produced by an American company, it may also be a deliberate change because in America, the word "Fanny" (pronounced the same as "Fannie") is a slang term for a person's buttocks.