Factual error: The movie takes place in 1977. A boy tells his father he is playing PacMan, which came out in 1980. Then we see a cabinet of Ms. Pacman, which came out in 1982.
Factual error: In the party scene Earth, Wind and Fire's song September is performed. The song was released November 18, 1978. The movie is set in 1977.
Factual error: The poster of Paul Simonon of The Clash in Holly's bedroom was neither captured nor made famous on the sleeve of 'London Calling' until 1979; the Nice Guys is set in 1977. (01:13:00)
Factual error: The guys are walking down Sunset Bl and behind them is a liquor store with the phone number on the sign. The phone number begins with 323, an area code which came into being in the late 90s.
Continuity mistake: When Holland shows the bartender the dollar bill in the shape of a shirt, he is smoking a cigarette before he takes the cigarette out of his mouth. Holland mentions to the bartender that he made it himself, with nothing in his mouth, but in the next shot, the cigarette is suddenly back. (00:09:45)
Continuity mistake: Russell Crowe is dunked head and torso in a pool, immediately gives chase to Blueface, but he's basically dry when reaches Holly. Later in the movie it's even worse, since Ryan Gosling has a near-death experience falling in a pool, but he runs as normal, only slightly moist in the hair (and even pulls out a cigarette and lights it later by the time the cops arrive).
Continuity mistake: John Boy draws the knife and makes his generous 'offer'. Cuts back to the Nice Guys who are driving fast; the Mercedes, as dirty as it is, is still perfectly intact with both sets of headlights working and the hood ornament. The front section was damaged when March fell asleep at the wheel earlier, and the car is again damaged when they pull over in the driveway. (01:24:10)
Continuity mistake: When Chet tells March "make a left here", he's pointing with his left hand. In the next shot his left arm is in a different position and he's pointing with his right hand. Moments later when he points at the house he lowers his arm but he's again pointing in the next shot that shows it is burnt down, and again even more blatantly after a close-up where his arm is all the way down. (00:29:20)
Continuity mistake: The two protagonists struck a deal to cooperate. Jackson is saying aloud the caption of a photo from a newspaper, holding it by the length while they walk in a longshot. At the cut he's holding the newspaper by the shorter side, and back to the longer side when they get back to the wider angle. (00:26:40)