When Beverly meets Flynn, she's in the chorus of a Gene Kelly musical (presumably "Les Girls") and he's starring in "Too Much, Too Soon." But that film was shot at Warner Bros. in Burbank, while Kelly was working at MGM in Culver City. It is impossible that they would have been working on the same lot.
In one scene Dakota Fanning is alone and you can see a electrical outlet behind her. It is a 3 wire grounded duplex outlet which did not exist in 1959. These outlets did not begin to be used until about 1963.
Errol told the people at the doctor's house during the last few hours of his life that John Barrymore just died. Barrymore actually died on May 29 1942; 17 years before Flynn died.
The film shows Errol Flynn going to New York to star in a play called "The Master of Thornfield." Flynn never appeared in a Broadway or Off-Broadway play and a play of that name was never produced on Broadway or Off-Broadway.
Florence refers to unsuccessful actors as "wannabes." That term did not come into usage until the 1980s.
The fiberglass automated entry gate into the studio parking lot would have been made of a solid piece of wood and been attended in the 1950s.
The green reflectorized street signs seen on the drive to Flynn's home were not available in the 1950s.
Florence refers to her book deal as a "slam dunk". That term was coined for basketball in the 1970's and later became a colloquialism for a sure thing.