At the very beginning of the film, the truck driver arriving to pick up the "horse" (elephant) was surprised to see the elephant that he'd just passed in the middle of a flat plain.
The orientation of the smashed roof shingles on the pool grounds changes from the overhead shot to the floor-level shot.
When Jack Conrad is on his balcony and approaches Manuel, a cigarette is in his mouth. In the next shot, a reverse shot, the cigarette is in his left hand. In the next shot, a frontal shot, it is back in his mouth.
When the Skid Row junkies confront Manuel, his back is next to the hill and in front of the crowd. In the next cut, as they chase Manuel, he is far from the hill and behind the crowd.
In the initial early cuts, when Nellie is a struggling actress, her final scene shows her crying from her right eye (which is recorded). In the completed scene on film, she is crying from her left eye.
In the beginning, Manny helps the truck driver carrying the elephant by towing him up a steep hill with his Ford Model T. The Model T could only handle steep inclines in reverse (it had better torque that way).
In '50s, there was still segregation for black people, but in the movie you see black people watching the movie at the movie theater in 1952 along with white people.
Traffic light in 1952 was not so bright as in the shot where the main character is in front of kine-scope studios.
Some scenes show ensembles and orchestras playing on the set during filming. That is entirely accurate.
The first party, set in 1926, includes lots of colorful party balloons, several years before they were commercially available. The party hosts, Hollywood insiders, most likely got the balloons from the studios.
If the first 12-tone work (Schoenberg Op. 25) was performed in February 1924, it wouldn't be unusual for Conrad to know about 12-tone musical composition 2 years later, in 1926.
A "Jackass Forever" billboard appears in the 1952 epilogue.
Jack pours a glass of Johnnie Walker Blue Label Scotch. Johnnie Walker Scotch dates to the 19th Century, but Blue Label was released in 1992.
Zhu is a common Chinese surname, but as rendered it reflects Pinyin spelling conventions for Mandarin Chinese, which did not exist until the 1950s. In the 1920s, it might have been spelled Chu, Joo, or some other way.
The "RADIO, SCREEN and STAGE" line at the top of Variety Magazine is in an "outline" font. Variety used a solid bold font in those years.
At the party at the start of the movie, when Manuel walks out if the house, a Jeep Wrangler drives in the back parking lot.
At about 0:36:00, Brad Pitt's car screeches to a halt on a dirt road. The tires screech like they're on asphalt.
When a record player is playing a record, the needle drags on the surface of the turntable, not on the record.
When Nellie finishes the line, "Cannot add, cannot spell," her mouth doesn't match her words.
About halfway through the film, at the end of the singing in the rain number, one of the extras shakes Torres' hand and says "Good idea" but his mouth just says "Good."