Factual error: There seem to be modern "Walk" and "Don't Walk" signs at each intersection. This film is supposed to take place in 1952. Also it is mentioned there are "Stereophonic" consoles in the motel rooms. Probably would not find those until at best the late 50s.
Revealing mistake: When Krampus walks toward Max after he yells at him to give him his family back, wires are controlling Krampus' arm. (01:24:30)