The film depicts Orson Welles meeting William Randolph Hearst whilst a guest at the latter's home, San Simeon. In reality, Welles never went there, and never met Hearst until after Citizen Kane (1941) had opened. (Their one, brief meeting was in a San Francisco elevator, according to Welles; there were no others present, and it may be that Welles made up the story and never actually met Hearst).
The film shows RKO production chief George Schaefer announcing to Orson Welles and Herman Mankiewicz that he has lost his job on the very day of the opening of Citizen Kane (1941) in May 1941. In fact, Schaefer did not get fired until late in the following year, and this was less because he had promoted the film career of Orson Welles than because almost all the films RKO had made during his tenure had been flops.
In the fictitious scene where Orson Welles has dinner at San Simeon, he tells the other guests that he was, as a teenage boy traveling in Europe before beginning his acting career, taught the art of bullfighting by the great matador Manolete. As Manolete was two years younger than Welles and did not begin to achieve any renown in the bullring until after the Spanish Civil War (that is to say, at about the time this scene is supposed to be taking place), this is impossible.
As the film starts, John Malkovich as Mankiewicz is berating Welles because of his doomed ideas for movies: '"Heart of Darkness"? Million-dollar budget? No-one wants to see that!' A few years earlier, Malkovich had starred as Kurtz in Heart of Darkness (1993), an adaptation of Joseph Conrad's novel.
In the shot of Orson cutting the Citizen Kane script, one of Kane's lines is "Who knows what lurks in the hearts of evil men? The Shadow knows!" This was the classic introduction played at the beginning of every episode of Welles' famous radio program, "The Shadow".