The film was originally slated for an early September, 2012 release date but ended up getting bumped until January of 2013 so some additional scenes could be filmed.
The movie suggests that Mickey Cohen had Jack Dragna murdered in his own house, but in real life Jack Dragna died of an heart attack years later. The movie is set in the late 40's/early 50's while Dragna died of the heart attack in '56.
When O'Mara and Wooters are sitting on the porch, the bullet holes that surround the window frame have charred edges. That would have happened if the shots were fired point blank, but in the event they were fired from a substantial distance away, so there should have been no charring of the wood.
Mickey Cohen: You heard of Manifest Destiny? That's when you take what you can when you can. The greasers took it from the redskins and we took it from them. And I'm gonna take it all from you, Jack, and not just because I can. But because this is my destiny. Los Angeles is my fucking destiny, you motherfucker.