Factual error: When Holland March is swimming behind the bar with mermaids, "Get Down On It" from Kool and The gang is playing. That song did not come out until 1981 and the film is set in 1977. (00:39:50)
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)
Revealing mistake: Healy tears off the October 26 sheet from the calendar, and before the camera cuts away, it shows the October 25 sheet underneath it. That's not how calendars work. (00:11:25)
Factual error: The movie is set in October 1977, but Holland March is waiting in a line to fill his gas tank on an "even" day. The 'even/odd' rationing was instituted in California during the second oil crisis of 1979, in May. (00:06:30)
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)
Factual error: When Jackson and Holland are driving after leaving the burned down house, a billboard for Jaws 2 can be seen in the background, but the movie takes place in 1977 and Jaws 2 wasn't released until June 16, 1978. (00:32:55)
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: Jessica is on the phone and asks the person on the line "Richard something? Yeah." Holly in the background just puts her hand one one of the nearest cards, but at the cut she's moving her hand back from the top of one of her solitaire lines. (01:22:00)
Continuity mistake: When Russell Crowe says in front of the hotel "She's meeting somebody", the steering wheel is turned in a different way than you see later as he turns the wheel straight. (01:07:40)
Revealing mistake: Jackson is fighting with the older guy at the party. In their struggle, the gun fires once. Ryan Gosling turns around at the appropriate time, but half the extras react to the supposed noise a second late, some don't even do that. (00:48:00)
Continuity mistake: March realises he's sitting next to Robert Downey Jr. with a fake beard and quite dead. Notice his necklace, worn above the tanktop. In the rest of the scene the chain is above or below the shirt, randomly. (00:44:30)
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)
Continuity mistake: When Haley asks "Why not go straight to the police", Amelia has just a bit of her hair in front of her left shoulder, a greater portion of it in the next shot. (01:14:55)
Continuity mistake: When the older dude tells the protagonists "They can't talk to you, man, they're dead", his pen points down in the wide shot, up in the close-up. (00:28:10)
Continuity mistake: When Mrs. Glenn shouts at March for cussing, she points at him with her left hand. Next shot and she's pointing with the right. (01:31:10)