Corrected entry: When Monk's funeral procession is going down the street, the dog on Bill's porch appears to be a Doberman. The Doberman did not exist until the 1890s. Any importation from Germany to the US was not until the early 1900s. (02:11:30)
Factual error: In the scene when Bill is throwing knives at the girl, right after he comes off the stage, the flag that drops as the band comes out has 50 stars on it.
Suggested correction: The flag in the movie has 34 stars in it. Thank you for great observation.
Continuity mistake: In the opening scene, priest Vallon cuts the right side of his face with the straight razor. Later on, when Bill and Vallon are belittling each other before the brawl, there is a scar on the left side of Vallon's face.
Suggested correction: In the first shot he was shown in the mirror.
Continuity mistake: The scene where Amsterdam is climbing on the Portuguese ship, we see that there are still four people left in the small boat and we see that Johnny is the first one on the ship, so how did the rest of the gang board the ship before Johnny and Amsterdam? They even know that the ship has been ransacked. (00:39:05)
Suggested correction: There was no scene that shows Johnny was first one on the ship. There was a scene where he climbs before Amsterdam who was the last on the ladder, and all the gang at that moment was already onboard, because they climbed there offscreen.
Continuity mistake: When Amsterdam tries to kill the butcher and fails, the butcher straddles Amsterdam on a table and tosses a cleaver in the air. The cleaver rotates counter-clockwise so that the blade is rotating backward; however, when the cleaver lands, it is rotating clockwise so that the blade sticks into the wooden table. This would be impossible the way the cleaver is tossed into the air with a back-handed flip. (01:42:15)
Suggested correction: It is possible, if it falls quick enough. Doesn't matter where it rotates, if it is blade down at the moment of touching the table - it will stick.
Revealing mistake: In the beginning of the Five Points battle it happens very often that people get hit badly with a sharp weapon but don't receive any wound. Watch for example in slow-motion how Bill sets out to mow down victim after victim with his cleaver. Later into the fight it becomes a lot bloodier, and sometimes the blood seems to come out of the weapon (e.g Monk's club seems to have a generous blood reservoir). (00:08:15)
Correction: The dog in that scene is not a Doberman but a Beauceron, an ancient French breed of herding dog from which Dobermans were bred.