Factual error: When Hooker comes out of the diner there is a billboard advertisement to the right. It is for Ezra Brooks bourbon. Ezra Brooks brand wasn't created until 1957.
Factual error: When Lonnegan brings the briefcase full of money to the cage for his big bet, all of the 100s in the case are 60s federal reserve notes, which obviously did not exist in the 1920s or 30s.
Factual error: The Helvetica typeface, used on the 43rd Street 'L' platform is not correct for the period of the film.