Factual error: When the hot air balloon comes down with Carrie in it you can see N410AA printed on it. This is commonly called a tail number on planes and is issued through the FAA, which of course did not exist during the time period of the episode.
The People vs. the Fonz - S11-E11
Factual error: When the Cunninghams are talking about Fonz's trial, Mr. Cunningham can be seen wearing a digital watch. Digital watches didn't exist in the 50's.
Factual error: There is no physical way that Steve Austin could perform most of his superhuman feats of strength in the ABC television series, due to the fact that they simply replaced his arm and legs, but didn't rebuild or reinforce the rest of his skeleton and muscles to handle the physical loads. Interestingly, author Martin Caidin (creator of Steve Austin in his novel, "Cyborg") actually did describe an incredibly complex whole-body rebuild that included vertebral reinforcement and ribcage and pelvis replacement, which was far more scientifically-accurate than the subsequent ABC television interpretation. ABC only accepted the series on the condition that it was less technical for their audience.
Uniform Day - S6-E17
Factual error: It is Uniform Day where they all have to wear their uniforms. The badges they all wear are those of patrolmen. The problem is that they are detectives and the NYPD has detective badges, which are distinctly different looking.
Horror in the Heights - S1-E11
Factual error: Outside the Indian restaurant, the street curb is painted red. In Chicago, throughout the 1970s, curbs were painted white or yellow to indicate special parking zones; never red.
The Countess - S1-E4
Factual error: Two cops (the bowtie guy that cuffs Rockford and the one that watches him being taken away from his trailer) report to HQ saying that the protagonist is a suspect for a 157, to which Rockford reacts saying he did not murder anyone (and it is in fact what he is accused of). But homicide is in CA police code 187, not 157. A 157 is an entirely different felony. (00:21:00)
Suggested correction: Wasn't Mary the one in the balloon?
Mary was in the balloon earlier in the episode with the man who runs it but near the end, Carrie wondered off into it and it took off with her inside ALONE.