Continuity mistake: At the protest, the 'dead' girl in orange talks to the two protagonists; her left arm is in a different position between close-up and full view of the staircase. (00:27:50)
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)
Factual error: Holland and Jackson drive in 1977 from the protest to the next hint to Amelia's whereabouts, passing through the Chinatown Gateway Monument, which was built in 2001. (00:29:10)
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: When March puts down the potted plant inside the charred house, Chet in the background is next to a shelf. He's approaching the same shelf in the next shot. (00:29:45)
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: When the odd couple stops the car in front of the billboard, the Mercedes all of a sudden has a broken light and misses the hood ornament it had when they drove to the burnt house, and that it still has when they drive to the party. This damage happens in a much later scene. (00:33:10)
Continuity mistake: When March pulls over in front of the billboard for "Pornocchio", his right hand is back on the top of the wheel in the reverse shot, it wasn't before the cut. (00:33:10)
Factual error: March is already wasted at the party, and tells the barman that "it's the killer bees." In the background as he says those lines (and even better when the dancer gets on her knees) you can see a bottle with half its label torn. That's because you can still make out from the bottom (and the shape of the bottle) that it's a bottle of the premium variety of Beefeater gin, Beefeater 24, which was launched only in October 2008, a good three decades after the supposed year of the movie. (00:38:20)
Continuity mistake: When Healy holds the pinstripe suit in the changing room, his thumb is on the label in the wide angle, it's not in close-up. (00:39:10)
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)
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)
Other mistake: The Nice Guys have just dropped the disfigured body onto the fancy dinner table of someone. They run away, but before the camera cuts away you can see Ryan Gosling is trying hard not to laugh. (00:47:15)
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: Holland March shows smugly the ad for his agency on the fridge. The note is hanging from the clip differently in close-up than the other angles. (01:05:25)
Factual error: To show how March was plenty wrong in his deduction about airport traffic, a big plane flies above his head. The plane has the trademark modern South West bright blue livery, but in 1977 it would have the Desert Gold colors. Or no colors at all, since South West didn't serve Los Angeles until 1982. (01:07:20)
Continuity mistake: When Russell Crowe and Ryan Gosling take most of the frame having the conversation in the car about the overflight curfew, the car is missing the rear mirror that it has before and after. (01:07:20)
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)
Continuity mistake: When the Nice Guys are avoiding the police that is arriving at the crime scene at the hotel, in one shot they take a sharp turn, no rear mirror present, which comes back when they hit the brakes a moment after. (01:11:35)
Continuity mistake: Amelia falls off the car after shooting once. She is lying one way in the wider angle, but when the two protagonists approach her, she's lying a different way, on one side. (01:12:15)
