Revealing mistake: When the bald guy robber first takes out his gun and begin shooting at the ceiling, it's obvious that he shooting blanks as when they pull back the shot, there is not one bullet hole in the ceiling anywhere along the subway car. (00:12:00)
Revealing mistake: Just as the train with the mayor starts moving, the film crew is reflected in the windows. (00:19:00)
Revealing mistake: After Garber shoots Ryder, he is told by the approaching policemen to "drop your weapon". At which point the camera pans to a shot behind Garber where he is holding the gun in his right hand and proceeds to drop it. Watch the bottom of the screen and you will see Garber catch the falling gun with his left hand.
Revealing mistake: The police car that transports the money is not what is used in actual police work. The all dark blue and white accents you see in the film is a color-scheme used in traffic cars and school safety cars. The real police cars are white with dark blue accents.
Answer: The hijackers did notice it. There's a scene where they notice it: look at the girl on the screen and then laugh. They get kicks from toying with people, which is why they didn't smash the laptop and just let the guy keep using it.
You're probably right.