Revealing mistake: In Garabedien's office, supposedly in Boston, the top shelves are full of the Dominion Law Reports, all Canadian legal cases, with the Canadian publisher's name prominently displayed. Below that is long shelf of environmental law reports, an odd thing in a criminal lawyer's office.
Other mistake: The bank clerk with the grey hair, offering the cigarette and sitting back is supposed to work in "the late 70's" according to the narration. Surprised to see him again in the audience (front right) of the panel discussion on March 14, 2008, some 30 years later, looking not a year older. (00:01:35 - 01:53:40)
Other mistake: When Otto Preminger calls Trumbo from his car to announce that Trumbo's real name would be credited for Exodus, Preminger tells him to look at the front page of the New York Times. The problem is that Trumbo has already picked up the paper from his counter and is reading before Preminger even tells him which newspaper features the article.