During the scene in the theater screening The Man Who Laughs, we see the beam from the projection room. It is shining out of a single window. In the '40s, theaters used two projectors and changed reels (alternating projectors) every 20 minutes or so, unlike modern theaters that use only one projector per screen. The back wall should have shown two projector ports, two viewing ports for the projectionist and a large port for the spotlight.
During Bucky and Lee's stakeout, when Bucky chases a portly suspect down the adjacent alley and tackles him, the stack of old tires that cushions their fall is clearly made up of modern, low-profile radial tires, including one 60-series sports tire in the center background that's so low and wide that it's standing up all by itself.
Handcuffs never had belt attached cases in the 1940's; they simply hung on the officer's belt. The cases used to carry them were introduced in 1960, and they were introduced in California before being used by police officers nationwide.
At the beginning of the movie, set around the 1942-3 Zoot Suit Riots, Bleickert hands his father a model and says "C'mon Dad, you haven't finished this model yet." From the shape of the wings it is clearly a P-47 Thunderbolt, but the shape of the fuselage shows that it is the later 'bubble canopy' model P-47 G or H, which did not fly until late 1944.
Modern red-background STOP signs appear throughout the movie. Red-background stop signs were not standardized in the US until 1954. For many years after that, drivers' training manuals said that STOP signs could have red or yellow backgrounds.
Everyone, including characters who have lived in the city for a long time, pronounces Los Angeles with a soft g, the way it is pronounced in modern times. In the early and mid 20th century, locals preferred the hard g (closer to the original Spanish name) so it sounded like Los Angle Iss. Although the original pronunciation was losing out by the 1940s (due to an immigration of Easterners such as Elizabeth Short who were unfamiliar with the name), it was still in use and can even be heard in a few movies and radio programs made as late as the 1950s.
When Ramona Linscott thrusts her utensils into her food, a small potato rolls onto the table and stops beside a glass. In later shots, the food has changed position and the wayward potato has disappeared.
Characters who knew Elizabeth Short refer to her as 'Betty' constantly. Though Elizabeth Short was known during her childhood as Betty in her hometown, she used the name 'Beth' not Betty throughout her stay in Los Angeles.
Cars are seen with 1945 an 1946 California front license plates - black and white with a white strip on top. In those years (and no other year), California only issued rear license plates due to wartime metal shortages.
Elizabeth's friend, who acted with her in the lesbian movie just before Elizabeth died, has a fully developed copy of the movie. How did she get the undeveloped film? When did she get it? And if she had no money, how did she get it developed?