Other mistake: The gang gets separated after an intense cop chase through the subway station and Cochise, Rembrandt, Vermin escape aboard a train and end up in Union Square. The guys step out onto the corridor to an empty platform, as Rembrandt comments that nobody has shown up. Vermin then grins and says "Something else just showed up!' as a gang of girls suddenly appears, standing by a stairwell, that wasn't there, across the tracks, in the same direction. (00:50:50 - 00:51:55)
Other mistake: At the end when the Rogues show up to see if the Warriors want to play, Swan says he'll lead them to the sand. He asks the rest of the crew if they're all packed, and when Snow asks the same, Swan pulls out a switchblade. Where did he get it? They were supposed to be unarmed when they headed up to the Bronx. If he broke the rules and had it the whole night, I would think he might have pulled it earlier while bopping his way back to Coney.
Other mistake: When Cyrus is shot by Luther, leader of the Rogues, he is shown at the wide angle, as slumping backward by the force of the shot. But in the following shot, unrealistically 'busts' backwards through the wooden platform behind him. Purely for dramatic cinematic purposes, when he should have just slumped to the floor.