In the TV special, the Cratchits repeatedly wish for a Christmas tree. In 1843, when "A Christmas Carol" was published and presumably takes place, German-style Christmas trees had just been introduced to England by the royal family, and would have been unknown to working class people such as the Cratchits.
In the TV special's finale, the song "We'll Have The Lord's Bright Blessing" is repeated. During the chorus, the soundtrack has claps on the off-beats, but the animation shows the characters clapping on the on-beats.
In the TV special, at Fezziwig's Christmas party, the speed of the fiddler's strokes do not match the tempo of the music.
The story of A Christmas Carol is presented as a play within this animated special, yet many of the occurrences would be impossible to pull off in such a medium. The "sets" would need to be far larger than the stage could accommodate, and the feats of the Ghosts would not be possible on a stage.
The Ghost of Christmas Past tells Scrooge he has one more shadow (vision of his past) to show him, then disappears and the Ghost of Christmas Yet-To-Come materializes. This was a line from the book before the Ghost of Christmas Past showed Scrooge what had become of his former fiancée, Belle, but that scene was cut from this adaptation, leaving the Ghost to announce a shadow that didn't happen.
In the TV special, the Ghost of Christmas Present takes Scrooge to Bob Cratchit's house just before Cratchit arrives home from church with Tiny Tim. Tiny Tim can be heard off-screen laughing, indicating they are home. The Ghost of Christmas Present then opens the door to the house to allow Cratchit and Tiny Tim to enter. Cratchit and his family do not have any reaction to this odd occurrence.