At the Panama Club, Eddie's glass of milk and the other two drinks disappear from the table just before the table gets flipped over and the brawl sequence begins.
When Jean is singing "It Had to Be You" as Eddie and George hijack trucks from a warehouse, Panama is sitting at a table with her hands folded in front of her. The only thing on the table is a drink and what appears to be a centerpiece that could be a candle. Jean walks and sings her way through the audience past Panama, until Jean's body blocks the camera's view of Panama for a brief moment. When Jean then takes a step, Panama can be seen for a split-second smoking in the darkened background. She was not holding a cigarette and there was no smoke from one in an ashtray, as Jean passed the table. A few moments later, when the song ends, there is a cut back to Panama, and she again is sitting in her original pose with hands clasped in front of her.
When Eddie returns to the club after the shoot out with Nick Brown, Panama informs him that Jean quit the club. However, in the following cut, when the bartender asks Panama if Eddie knows that Jean quit, she answers that she doesn't think so. Update: judging by the little smirk Panama gives the bartender, it's as if she's daring him to say something to Eddie about Jean.
When Eddie goes to the garage to ask for his old job back, he addresses the boss as "Mr. Fletcher". However, on the closing cast list, the character (played by Joseph Crehan) is credited as "Michaels".
Eddie's arms change position when he falls on the church steps.
On November 11, 1918, while Eddie, George, and Lloyd are shooting at the enemy, George says, "Prohibition law goes in next year." How would anyone know that then? By November 11, 1918, only 14 of the 36 states needed had ratified the 18th amendment. The 36th state, Nebraska, ratified it on January 16, 1919, giving the US one more year before prohibition went into effect on January 17, 1920. Granted, New York state was partially "dry" by 1918.
The women's costumes, makeup, and hairstyles follow the fashion of what was popular in 1939, not in the twenties when women wore their hair very short (as one of the newsreel clips shows) and painted their lips to look very small and round, instead of following the natural lip line as in subsequent decades.
At the beginning, the announcer claims that almost 1 million American were on combat duty in April 1918. This seems to be a slight exaggeration, the AEF's first noteworthy operation took place near Cantigny towards the end of May 1918, and the number of almost 1 million had not yet been reached in April.
When Eddie and his men impersonate the Coast Guard, there's a miniature shot of the two boats pulling alongside each other. Nick's rum runner boat that George captains is a much taller boat and its deck is higher above the water than the smaller vessel. Yet when the shot changes to live action and Eddie's crew is throwing mooring lines across to the bigger boat, the decks are now the same height; furthermore, when the men cross from one boat to the other, they merely step over the rail instead of needing to climb up to the taller boat's deck.
The head-shot of Eddie Bartlett shown in close-up on his New York City Taxi license card, seen by Jean when she gets into his cab, is obviously a still photo taken during the filming of that scene, with the card closeup edited in later. He is wearing not only the same cap in both the scene and the ID photo, but also the same crooked tie, the same facial expression, and a vertical seam from the back seat upholstery is visible behind him.
When Nick Brown ducks behind the end of the bar, a bullet strikes the bar and chips off a piece of wood. The resulting bullet hole in the bar not only looks like a perfect hole made by a drill, but it is at an impossible angle, based on where the shooters are hiding.
When the gangsters hurl bombs at a storefront from the car, the prop explosives bounce off the building and roll into the street before the blast. Furthermore, that same footage was seen in the film Angels with Dirty Faces (1938).
(at around 1 min) As the former sergeant (now a security guard) is locking up a gate after letting a car pass, the background is clearly a painted set (including phony light fixtures in 2-D).
The film is full of classic songs from the 1920s, but the arrangements and vocal styles are those of 1939. No attempt is made to reproduce the sound of 1920s dance music.
After Eddie sells George his taxi business for $250,000, he slides downhill and is seen having to drive a taxi himself and then becoming a drunken bum. No explanation is given of how Eddie loses this money, which would be the equivalent of more than $3 million today. At the time he sells the taxi business, he also owns another business. Perhaps he sold the second business as well and lost all the money in the stock market (he sold the taxi business so he could use the money in an attempt to save his holdings when the market collapsed), but we are never told. Facts and logic have apparently been sacrificed to the censor's insistence that the audience must be shown that crime does not pay.