Holland March yells for someone to call 911. It was 1977-78 and while 911 was an emergency system that was used as early as 1968 in Alabama, it was not formally introduced to Los Angeles until October 1, 1984.
The movie takes place in the Fall of 1977, but there are multiple songs heard being played in various party/club scenes which were released in 1978 ("September" by Earth, Wind & Fire), 1979 ("Escape: The Pina Colada Song" by Rupert Holmes, "Boogie Wonderland" by Earth, Wind & Fire) and even 1982 ("Get Down on It" by Kool & The Gang).
About 30 minutes into the film the main characters are seen walking out of city hall. There are two LAPD officers on guard duty. They have magazine pouches for semi-automatic pistols on their sam brown belts. LAPD carried revolvers in the 1970s. They should have speed-loader pouches.
A red 1976 Cadillac Eldorado convertible is prominently displayed at the "1978" Auto Show. Not only would the 1976 model be three years old by 1978, but Cadillac famously discontinued its Eldorado convertible option in 1976.
The reporter, during the interview with the Detroit Auto Manufacturer's representative mentions the "big three." In 1977, the US auto manufacturers were referred to as the "big four," and would be until Chrysler acquired AMC in 1987.
While Healy and March are driving to the airport, a blue Southwest airplane passes over the freeway. However, the color scheme seen wasn't used until 2001; around the period the film is set in, the airplane would've been colored mustard yellow. In addition, Southwest Airlines did not service Los Angeles until 1982, 5 years after the film is set.
Holly's bedroom has posters of the band Blondie on the wall. Although Blondie existed in 1977, they were virtually unknown in the US outside of the New York punk/new wave scene. They did not become widely known and popular until their breakthrough single, "Heart of Glass" released in January 1979. The logo used appears to be post-1979.
Several of the vehicles at the auto show scene are incorrect for the 1978 model year. For instance, the Cadillac Eldorado convertible went out of production for 1976 (which GM promoted heavily). And, although the Avanti was still available as a limited production specialty car, it would not be positioned with major manufacturers like GM, Ford, and Chrysler.
Despite this film taking place in 1977, a poster for Jaws 2 can be seen; even though the movie didn't really come out until next year, plus advertisements wouldn't have been feasible for a movie, that's not yet been released during that same time.
As previously mentioned, the poster for the The Clash album London Calling is seen on a bedroom wall, 18 months prior to its actual recording sessions and 2 years prior to its official release. Furthermore, the poster itself is a concert photograph from September 20, 1979.
In one of the outdoor party scenes, the song "Boogie Oogie Oogie" by A Taste of Honey is being played in the background. This song was not released until June 1978, whereas the movie takes place in the fall of 1977.
(1) Killer bees are discussed at one point. Though these hybrid bees were present in South America from the '60s, no one in the US had heard of them until the 1980s, and the first sighting was in the '90s. This film is set in 1978.
(2) In the car show, a 1978 or '79 Cadillac Eldorado convertible is displayed (and later blown up), with a voice over description of a "7 liter V8". However, American car engine sizes were measured and advertised in cubic inches well into the 1980s. It wasn't until Japanese cars began to dominate the American car market (with their engine sizes commonly measured in liters) that American cars followed suit. Also, 7 liters is about 428 cubic inches, so the reference is probably to the 425 V8, introduced in 1977. In the early '80s, Cadillac, in response to the gas crisis of the late '70s (also shown in the film), began to downsize its car engines.
A Southwest Airlines 737 is shown landing in Los Angeles. Until the later part of the 1980s, Southwest was in fact limited to flying within the state of Texas and to neighboring states. It did not fly into any Los Angeles area airport until at least 1988.
During Holland March's search for Amelia Kuttner, the Bourbon Bartender recognizes her and claims that she was at the bar recently, drinking "Bourbon Martinis," to which March responds, "Well, that's disgusting." A Martini is a cocktail composed of Gin and Vermouth, plus a few shakes of bitters (optional). Changing the Gin to Bourbon (or Rye), a bartender would be making the classic Manhattan cocktail, which is quite tasty. This cocktail is never referred to as a "Bourbon Martini," and any bartender worth his wages would know this.
Near the end, Holland falls in a pool fully dressed and gets soaked. Shortly after he pulls a paper cigarette packet out and lights one. The packet and the cigarettes (as well as his suit) are bone dry.
One of the headlights was broken on the Mercedes when it hit the water barrels, and later the bottom headlights are both on and the top two off. When March and Healy are driving to March's house, the top two headlights are on again and the front of the car is undamaged, but when they arrive the front is damaged again with the broken headlight, bent license plate, and the bottom two headlights on.
Jackson Healy's blue Oldsmobile Toronado sometimes has a rear-view mirror on the windshield and sometimes does not have the mirror during the same sequence of driving. For example, when he is driving Holland March to find Amelia at the Burbank Apartments, the Toronado pulls up to the curb with the rear-view mirror on the windshield. As they pull away to drive to the airport, the closeup of the front of the car shows no rear-view mirror. Next as they approach the Westin Hotel, the wide-shot shows a mirror again. But when the camera cuts to another closeup of the two men talking, the mirror is gone again. Ironically, March's Mercedes convertible always shows that it has a rear-view mirror, even when the camera closeup only shows one of the men speaking.
If the film is taking place in the autumn (as denoted by 1978 auto show), there should be many advertisements for Star Wars: Episode IV - A New Hope, which was the most sensational hit during 1977. Yet, none of them was shown in the film.
In the first shootout with John Boy, Jack's automatic runs out of ammo and locks open. He asks Holland for his gun a revolver which Holland tosses through the window and then brings a cookie jar full of ammo to Jack. Jack is next seen reloading a revolver instead of the automatic and firing out the window.
When Holland smashes through the glass roof, the glass breaks without him actually 'touching down'. He maintains the posture he had while falling and just passes through while the bits are flying, revealing the scene to be CGI.
When Mrs. Glenn came to the March's house (exactly at 1 hour 30 minutes 20 seconds) we can see a blue necklace that is partially hidden under her dress. Then several seconds later we can see this necklace over her dress, then again under her dress and over it. However she didn't touch the necklace.
During the fight with Jackson, John Boy gets rid of his jacket as a hand grenade inside the pocket is about to explode. In a following shot, when Jackson pounces on him, he wears his jacket again. Once more in a subsequent shot, being pinned down to the ground, he is shown without the jacket.
The plot calls for the porno to be spliced into the middle of another movie; then only a couple of minutes later, the same film has been spliced back out of the movie and rolled up in its original canister.
When Holland March finds Sid's body, he rolls away and pushes on the ground with both hands to stand up. As he does, you can see the "cast" on his left arm flex around his wrist, rather than remaining rigid like a real cast would.