Other mistake: Another note about Clark's falling through the ceiling and onto his son's bed: Take note of the shot of him in the attic after falling through the ceiling. He's standing on the upper bunk of the bed now, but from the shot in the attic, he's only down to his knees or so. Assuming his home's ceiling joists are 8 inches or so, then the mattress of the upper bunk would have to be no more than, say, 10 inches from the ceiling for that much of him to still be in the attic while standing on the bed. I've never seen a bunk bed whose upper bed gave you less than a foot of space between mattress and ceiling! (00:33:05)
Other mistake: Up in the attic when Clark finds the videos, the video he watches is labelled Christmas '59 but while watching it, the sign being held up says "XMAS 1955"
Suggested correction: It may be a 2nd film he watched after the 1959 film. This may not be in real time, just like we only see Clark in the attic for a few min but in reality the family was gone assumingly much longer than we saw on film and Clark was there longer than we see.
Other mistake: After we see the cat pulling on the strand of white Christmas tree lights, there is a close up shot of the electrical outlet with one cord plugged into it. When the lights go off, both the colored and the white lights go out at the same time. Clark has to plug in two cords to make both sets of lights come back on. Either the colored lights should have been out to begin with, or both strands of lights should have come on with one plug. (01:09:05)
Other mistake: When Clarke and Eddy are drinking eggnog by the tree, and Snots is drinking the tree water, look at the tree's trunk. It's a birch tree not a pine.
Other mistake: When the lights don't work, Clark punches Santa and knocks the antlers off the reindeer. When the lights come on and the family comes out, the antlers are back on their heads.
