The phonograph used is a Guild "Graphanola" - a hi-fi made to look like an outside horn machine. These were built in the mid 1950's when Hi-fi was the newest sound technology, almost 30 years after when this movie is set. A non-electric inside horn machine like a Victrola would have been more than likely used in the late 1920's, as outside horn machines were outdated by then.
In all of the films screened, the THE END title dissolves onto the screen, either over the action or as a separate card. This practice did not begin until the early 1940s; prior to that, all films simply faded to black, then faded in on the end title (the only exceptions being gags, such as a character walking onscreen holding a sign reading THE END).
In the filming for the start of the sound era, a noisy "unblimped" motion picture camera is shown doing the shooting. Early sound movies would have used either an enclosing thick metal "blimp" to mute the camera noise, or a noise-deadening booth containing both camera and cameraman.
While autographing photos for George, Clifton uses what appears to be a Parker Streamlined Vacumatic fountain pen which did not exist until 1937. Other pens used in the movie appear to be European pens from the 1940s.
In the early part of the film an issue of Variety is shown, with the front page covered with photos. Photos were allowed in Variety only in advertising copy. After 1920, it was an important style point of Variety that the publication never used photos on the front cover. They re-introduced photos as late as 1988, when the Silverman family sold Variety to Cahners.
(at around 1 min) The 1950s-era record changer is shown "playing" a 1930s-era 78rpm disc, but rotating at only 45rpm - a speed developed for use with the 7-inch vinyl disc format which would not be introduced until 1949.
When George meets Peppy for the first time he is surrounded by reporters and photographers. One reporter has the typical "PRESS" card stuck in his hat brim, but the typeface is Helvetica, not introduced until 1958.
When Valintin destroys his film prints he opens can after can of film and takes out reels of film. The reels have rolled edges and are the type manufactured by Goldberg Bros. or Tayloreel Co. in the late 1940's at the earliest. In the thirties film reels did not have rolled edges and a projectionist could burn or cut his hand if he tried to stop a rapidly spinning reel. Most reels were of a spoked design having 4, 5 or 6 "arms" or spokes. A few reels were manufactured with circular holes but they usually had 6, not 5 holes. Further, the film cans he empties are "raw stock" cans, designed to hold film "off reel". The additional thickness of the metal reel would not allow the lid of the can to close making that type of can useless for mounted prints. Films on reels would always be kept in fireproof rectangular metal shipping cases. However, the public recognizes film "cans" better than shipping cases, which is probably why they used them in this scene.
When George wakes up from his nightmare, he is clearly propped up on pillows, almost sitting upright, with at least two pillows stacked vertically behind his head and shoulders. However, three seconds later, when he gets out of bed, the pillows are stacked horizontally, with one in front of the other and none of them are vertical.
Early on when Peppy dances through her quickie audition she places her purse on the ground immediately to her right. In the next cut, with the surrounding ground space in full view, the purse is nowhere to be seen. Then, dance done, the purse reappears.
In the restaurant scene where Peppy is giving an interview, there is a shot from behind where the person wearing the headset has just one ear covered by the headset. In the next shot from the front both his ears are covered.
Back page of Variety is full-page ad for Coca-Cola; ads in this trade paper were always for show biz-related concerns (studios, stars, agencies, upcoming productions) but never for traditional consumer products like soft drinks, cigarettes, cars, etc.
The pair of white porcelain 'art deco' figurines seen time and again behind Doris and used as a metaphor for George's and Doris' relationship aren't actually art deco or French, but made in Devon in the late 1970's by master ceramist Rod Hill.
During the montage of films starring Peppy Miller, the spelling of her name on the movie posters changes from Pepi to Peppy. This may be deliberate - it is not uncommon for those with small parts to have their names misspelled.
It is correct that the SMPTE leader shown did not come into use until television, but the writer says it should be Academy leader (Start..11..10..etc). This was not put into use until after 1930. The earliest sound films had a "Start" frame, but then just 12 feet of black film until the picture began.
In a hospital scene (1930 or 1931), Calvin Coolidge is pictured in a photo-portrait on a wall. Coolidge left the presidency in 1929. But of course that fact does not imply that his photo-portrait would never be seen on walls.
During the electrocution scene in the movie-within-a-movie ("A Russian Affair"), close-ups of the control panel show an odd mixture of Russian and English labels. For example, the label for the push-buttons reads "Washwater Flow."
In the movie-within-the-movie shown at the beginning of the film, Valentin's character is being tortured by the application of electrical shocks. While the "Russian" labels on the gauge and rheostat do refer to voltage and current (in what appears to be grammatically incorrect Russian), the the panel to the left of the gauge refers (in English) to "Washwater Pressure" and the gauge itself is marked (in English) as showing pressure in pounds per square inch.
When George Valentin sets his precious reels of film alight in his small bed-sitting room the resulting fire is far too tame. Nitrate film stock is highly flammable and would have burned more ferociously. Moreover there would have resulted highly toxic fumes which would have proved fatal quite quickly. (For a cinematic reference to the dangers of carrying film in public places check out Hitchcock's SABOTAGE)