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)
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)
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 the Nice Guys in the ending mention Lynda Carter, they are holding their smokes in entirely different ways between shot and reverse. (01:50:25)
Continuity mistake: When at the end of the movie Kim Basinger sits with the Nice Guys (well, back-to-back with them, kinda), March is already wearing the sunglasses that he puts on when she says "Boys, boys." (01:47:15)
Continuity mistake: John Boy throws his jacket in the street, but in the brief shot where Jackson tackles him he's still wearing it. (01:44:55)
Continuity mistake: When the older guy falls back and tries to drag Holly with him, she wiggles free leaning towards him, but in the reverse shot she's rotating the other way. (01:41:05)
Revealing mistake: In the shootout on the roof, the CGI blood spurts are phony, their light does not match the scene. (01:41:00)
Continuity mistake: Holly throws coffee on Tally, but her face and dress are clean a moment later. (01:37:30)
Continuity mistake: Mrs. Glenn drops by to chat about the case; during the scene, her large square necklace is under or above her dress, randomly. (01:30:15)
Continuity mistake: After the encounter with John Boy, March asks Perry a question. He says "They havent', and they are not going to." The sentence spans across two shots, with a visible gap in continuity in the way Russell Crowe puts his sunglasses on. (01:28:25)
Continuity mistake: There's a brief cut to Ryan Gosling saying the line "Okay, so it's like Jack the Ripper and then your mom, basically." Amelie doesn't move, but her hair changes position completely. (01:16:05)
Continuity mistake: The nice guys take Amelia to March's house and put her on the bed. She's lying on the bed, left arm stretched, green pillow shifted definitely towards the right. When she comes to, her arm is bent and the pillow is centered. (01:12:45)
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)
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: 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: 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)
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)
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)
