Revealing mistake: In the beginning of the movie, there is a scene where Buddy hits his head on the roof of the house as he's running out. You can obviously see a machine pushed the snow forward to land on his head. [May be easier to see in fullscreen version]. (00:12:40)
Revealing mistake: While we see Buddy drinking the entire bottle of Coke, it is quite obvious that he is not actually drinking it. Buddy has his lips firmly sealed around the end of the bottle and gulps down the entire lot. If he was drinking it, the bottle would have caved in as no air was getting inside. It was not even possible for him to blow air from his nose back into the bottle due to the fact that he is continuously gulping.
Revealing mistake: When Buddy is chugging the bottle of Coke, there is a shot taken from behind Buddy. Look at his arm when this is happening. The dark line running down his arm is the tube used to carry some of the Coke away, so Will Ferrell didn't have to drink the entire 2 litres.
Revealing mistake: Towards the beginning, in one of the scenes where Buddy is sitting on Papa-Elf's lap, you can see Bob Newhart is not quite lined up with Buddy, or his legs in the foreground (Which are actually the legs of a little kid), as he is really a short distance away, to make it look as though he is shorter.
Revealing mistake: When Buddy is in the mailroom dancing on the table, you can see the sides of his pants flare out around the hips to see the outline of the harness used when he's low to the ground during some of the dance moves.
Revealing mistake: When Buddy confronts the Department Santa (Artie Lange), watch the kid sitting on his lap. He's mouthing the words both Buddy and Santa are saying.
Revealing mistake: When Buddy is first seen walking toward Gimbels, the man in the costume is Will Ferrell's stand-in. His hair extends below the hat.
Revealing mistake: The number of snowballs the bullies throw at Michael and Buddy is very unrealistic. There are about five kids, and yet at any given moment, there are dozens, if not a hundred snowballs in the air.
Answer: Yes.