The California Highway Patrol squad car used to chase Duke was a 1974 Plymouth Satellite. The real California Highway Patrol used Dodge Polaras at the time. Additionally, the Federal Signal Corporation "AeroDynic" red and blue light bar on the roof of the police car was not invented until the 1980s and would not have existed in 1971.
When Duke is in his hotel room near the end of the movie, the camera pans across the television quickly, showing footage of an M1 Abrams tank. The film is set in 1971, but the first Abrams was not built until 1978.
Part of the movie is set at the Flamingo Hotel - this name is accurate for the time the movie is set. However, in an earlier scene in the movie, the signage/logo for the hotel in its 1990s "Flamingo Hilton" incarnation is clearly visible.
In the White Rabbit/Bathtub scene, after Duke locks Acosta in the bathroom, he crashes on the bed attempting to get some sleep. He pulls a large cardboard box over himself. There is a blue "closing the circle" recycling symbol clearly visible on the bottom of the box. Though that symbol had been created around 1970, it was not yet used, if at all, on cardboard boxes at the time.
When Raoul (Depp) is talking about being in The Matrix in 1965, you can see "Grace Slick" in the background singing "Somebody to Love". This version was released by Jefferson Airplane in 1966 when Slick joined the band. The original version, by Grace Slick and the Great Society, was significantly slower than the Jefferson Airplane cover.
Modern power lines visible: in the opening convertible scene, just after picking up the hitchhiker and around the point where Duke narrates "how long before one of us starts raving and jabbering at this boy..." and then again during, "Jesus did I say that?..." To the right and behind the hitchhiker on screen, modern power lines are visible along the desert road.
On the way to pick up their rental car, they are slowed down because a stingray corvette hits a pedestrian; it looks in the film like the vehicle (which crashed) has an integrated rather than a chrome front bumper; the chrome front bumper wasn't adopted until 1973, while the movie is supposedly set in 1971.
When Duke is in the desert, talking on the payphone at the junk yard, on one of the crane shot swoops, the footage was edited in reverse. Notice the smoke going back down into the smoking car, as well as the papers on the side of the phone booth moving quite rapidly.
When Duke and Gonzo drive into Las Vegas to the Mint Hotel there is a banner which reads: '$100,000 Mint 400'. However, at the actual race a banner reads: '$50, 000 Mint 400', which can also be heard by the announcer at the race.
When Duke is in the Mint bar, his cigarette is broken when he lights it. While he is smoking it, the broken part falls off. He spins around in his stool looking for his attorney, the broken part is there again.
In the scene in the Mint bar at the beginning of the movie, Duke inspects Gonzo to make sure he is not a monster. In the medium close-up, he turns his right shoulder towards the camera, while it should be his left shoulder like in the full shots.
In the North Star Coffee Lounge when Dr. Gonzo says he'll wait in the car with the lemon meringue pie, Duke picks up his plate from the counter and then changes his mind after looking at the waitress. The sky behind Duke changes from black to light blue between shots.
Just before Dr. Gonzo pulls out the hunting knife room service sent up, Duke's sunglasses instantaneously change from the purple-tinted pair that he wore in the previous scene to the yellow-tinted ones he wears throughout most of the film.
When Duke and Gonzo are stopped by the side of the road with the hitchhiker, Gonzo's watch changes between the shot where he says "What the fuck are we doing out here in the middle of the desert..." and "... We need help."
At the Mint Bar, Gonzo has his sunglasses on, but then in one shot Duke turns to Gonzo when he's mumbling, and he has his sunglasses off. Then it switches back to Duke, then back to Gonzo, and he has his sunglasses back on.
During the restaurant scene in north Vegas, the lighting outside changes four times. Most noticeably right at the end when Duke is leaving. Its dark outside while he stands at the door, but when after returning the plate, it is much lighter.
When Duke is checking in at the Mint, he stands in line holding his typewriter in his arms. When he gets to the counter, he is no longer carrying the typewriter, and places only the tape recorder on the counter. A few moments later, a wide shot of the counter shows the typewriter on the counter, propped up on the recorder.
After they pick up the hitchhiker in the desert Duke hits Gonzo on the neck from the back seat. After Gonzo regains control of the car the wind is blowing his shirt open, revealing a cable for his microphone.
White SUV visible in opening scene: in the opening convertible scene, just after picking up the hitchhiker and around the point where Duke narrates "...when my attorney starts screaming about bats..." in the closeup shot of the hitchhiker. Just before the shot changes, an out-of-place white SUV can be spotted the far right of the screen behind the hitchhiker, parked along the desert highway.
(at around 1h 04 mins) When the trooper is saying to Thompson that he should go to the rest stop and sleep, the camera follows him around the front of the car. But if you look at the car door in front of Thompson you can briefly see the shadow of a camera moving from the top of the hood and move backwards across the door.
During the Steadicam tracking shot of Duke and Gonzo walking away from the hotel at the start of the film, immediately after the dwarf employee is knocked over by the swinging doors, they walk behind some random cables that come into view on the right side of the frame at the very last second of the shot.
The film is set in 1971. The Ford Maverick was first introduced as a 1970 model. Even in the hands of Raoul, there's no way a car less than two years old would be that rusted and weather beaten. Dented and smashed, of course, but that kind of paint damage takes a decade or more.
The California Highway Patrol officer says that the town of Baker, California is outside of his jurisdiction. Although CHP officers are assigned to a specific office, technically the entire state is his jurisdiction.
In The Flamingo Hotel Rauol Duke looks in the peephole to check on Lucy. There's no way Duke can clearly see her. Peepholes can only be clearly seen looking from the inside (of the room) outwards (toward the wall and hallway).
While driving down the Vegas strip in the convertible on the way to the Debbie Reynolds concert, they pass Binion's Horseshoe Hotel and Casino twice. However, the scenes outside of the car are not meant to be realistic. It shows lots of casinos that are not in order, but this is from the mind of a drugged out driver - the car itself is floating in air the whole time.
In a few shots taking place in the Chevy's interior, you can see the car has white vinyl door panels from a 1973 or 74 Impala (or Caprice convertible), while the main "Red Shark" is actually a 1971 Impala convertible. The Impala had slightly different door panels for 71/72 than the 73/74, but was essentially the same car overall. Apparently another car was fixed up for use in the movie as a backup or secondary vehicle and used for some shots from the inside.
When Duke and Dr. Gonzo sniff the ether, Duke throws out his lit cigarette. A moment later, he has the ether soaked flag to his face and a new lit cigarette in his hand. For a drug connoisseur like Duke, it's highly doubtful he'd be smoking around ether fumes, especially since he had just earlier thrown out his cigarette to sniff.
While Duke and Gonzo are driving down the freeway during the first 15 minutes of the movie, there are several shots (mostly when the camera is shooting into the car from the front side of the windshield) it is clear that the gear shifter of the car is placed in park. When some shots alternate to the back of the car, facing forward, the gearshift is in the correct drive position. (This is most likely due to the majority of shots being filmed while the car is being pulled on a trailer.)
When they are stopping on the highway because of the bird-like hallucinations they stop on the side of the road. They soon speed up after that and the wheels make a screeching sound. Tires don't screech on dirt because there's not enough friction.