Revealing mistake: When Frank takes the orange juice from the tray Johnny 5 is holding, the tray moves with the glass for a second. This is because the orange juice glass was glued to the tray, so Johnny wouldn't drop it. (01:05:25)
Revealing mistake: Some shots used in the scene where Johnny runs from the Nova helicopter were shot using the small toy version of Johnny. There were no mountains in the area and a small version was filmed heading towards some big rocks with the camera on the ground to give the impression they were in a mountainous area. (01:30:15)
Revealing mistake: When Number 5 is leading Number 3 into the toilet and moves at the last minute, you see Number 5 falling over, but in the next scene, he's perfectly fine.
Revealing mistake: When Frank is knocked down with the tray, the arms of the person operating Johnny 5 are visible when the robot turns to run.
Revealing mistake: After Johnny blocks the gunshots from Frank, he begins to flip a coin and imitate John Wayne. You can see the thin wire connected to the coin on the left side of it.
Answer: There were always 5. You see the 5 during the demonstration. Then, before the lightning hits, we see 4 of them in line, but number 5 was still attached to the generator and not in line. When they go inside, there's a weird cut that makes it look like only 3 made the turn, but if you watch closely you can see there's 4 followed by number 5.
Bishop73