Among the differences between the Trueniverse and Toobworld is the timeline of historical events. For example, Jules Verne, as seen in 'The Secret Adventures of Jules Verne', is about twenty years younger than the real writer.
'Boardwalk Empire' has truncated a few events from 1920 (besides fictionalizing Nucky Johnson into Nucky Thompson). The big meeting between Nucky and gangsters Arnold Rothstein, Lucky Luciano, Johnny Torrio, and Big Jim Colisimo (seen counter-clockwise around the table) took place in January. Big Jim went home to Chicago and was killed with days of his return (at least as it appeared in the series debut episode). But in the real world, he wasn't murdered until May of that year.
The second episode opened with Big Jim's funeral in Chicago, and it was snowing. Granted, it's the Windy City and it's supposed to be pretty cold out there, but a snowstorm in May seems to be pushing it. Besides, later in the episode, Jimmy Darmody's wife mentions that Christmas was only a month before.
Something to keep in mind whenever you see something in a TV show that you don't think would have happened or had happened in the real world: it ain't the real world!