Factual error: In episode 2-21: "Creatures of the Night," Mike and Kelly are at the theater watching "Rocky Horror Picture Show" in 1977, talking during the song "Sweet Transvestite." After the line "satanic mechanic" and the audience callback "S and M.", which is only about two thirds of the way into the song, the music suddenly crescendos and ends, to be replaced by the song "Touch-a Toucha-a Touch Me," which occurs several scenes further into the movie.
Factual error: In episode 55 "The Perfect Day" they show a 1965 flashback of a blue Philadelphia Police car. The Philadelphia police didn't go to the blue cars until 1973 when Mayor Frank Rizzo saw that New York went to the blue cars and liked the color. Before that the cars were red.
Continuity mistake: In Episode 90, "Torn" from Season 4 (4/8/07), at the end of the episode, when Elizabeth Stone is arguing with her daughter at the top of the stairs, her shawl goes from around her arms, to across her back, to completely gone several times from shot to shot.
Factual error: In the 5th episode of season 5, "Thick as Thieves", look at the area by the door when we see Margot and Spencer in the hotel room in 1989. The light switch is a flat "Decora" switch, and above the door handle is a black box that houses electronics for a "card key" system. The light switch was not introduced until the 1990s, and while the card key system was introduced in 1985, only very expensive hotels afforded the conversion costs - and the hotel they're at isn't exactly the Hilton.
Factual error: In a flashback, Danny is depicted as listening to the Dean Martin song "You're Nobody till Somebody Loves You" (indicated by the change in volume when he opens the door for his parents) which wasn't released until November 1964, two months after Danny's portrayed death in September 1964.
Continuity mistake: At the start of the episode the date "October 23, 2003" appears onscreen, which is the night of the party where Laurie Dunne died. However, shortly after, we see the officer typing up the accidental death report and the year of death reads as "2004" and also later when Laurie's father shows the laptop to Stillman and Lilly, we see the date stamp "2004:10:23" on the image that Laurie had emailed.