Shortly after Trumbo writes the script for Spartacus, he meets Otto Preminger, who says that he is "the director". It sounds like he is claiming to be the director of Spartacus, and this is why he has a copy of the brand-new script.
In real life, Spartacus was directed by Stanley Kubrick, who was never mentioned in Trumbo.
Was the movie intending to say that in the story of the movie, Otto Preminger directed Spartacus? If so, is there a known reason that they changed this particular detail from real life?
Or, was Otto only intending to mean that he was another director who wanted to work with Trumbo? I don't think it ever actually shows him on the set of Spartacus directing. But if this is the case, then how did he end up with a copy of the Spartacus script so quickly?