Other mistake: In a city of millions and millions of inhabitants, when the protagonist chases his neighbour till she enters the building in William Street, the taxi that passes in front of him as he crosses the road is the same taxi with license plate T 9362 that nearly ran him over at the very beginning when he was trying to get his sign back. Which incidentally is a model of Chevy Caprice post-1981 (likely a 1987 Caprice). (00:02:25 - 00:24:35)
Other mistake: Arthur watches Murray's show in the hospital room, he is able to see himself in the Pogo's Comedy Club performance. Forgetting how very contemporary this whole "viral video of person making a fool out of himself" dynamic is, and how astronomically unlikely it is that there would be taping of some open mike session in a club, it still makes in fact sense that there could be a recording of Arthur's performance, since there is a monitor backstage and in an earlier scene there was a guy with a camera on a tripod far in the back of the room when Arthur was taking notes. But in the video shown during Murray's opening there are 2 different angles of the performance, which are also different from the one show in the monitor backstage. Amateur night with 3 cameramen and a director/editor? Come on. (00:59:50)
Suggested correction: They purposely stuck the images in a way that it repeats itself over and over again. It's intentionally made in a way of not flowing straightforward.