1980s AVTEL 4 colour mechanical display, how is the pixel state reset?
There are many ways it could be done. Knowing how it was done requires prior knowledge or some who is clairvoyant with period engineering tools.
Most likely there was an array of stepper motor driven actuators like those used on 8” floppy drives each with a home position optical sensor also used in 8” floppy drives for the Track 0 and sector 0 optical sensing.
The heavy duty chain would pull the array as the computer sends the required pixels with several rows at a time in advance of clearing the position much like a inkjet printer does many rows of pixels at a time from one scanning head. except this was a full line scan of several rows of pixels that had to be gently turned to the next rotational position counted by the next display change in pixel rotations.
So 007 would appear after a minute of mechanical flips energized by some magnetic   motor for the number of rotations required spinning wildly in a clicketty-clack of changes.
Game shows used bicolour  similar but different pixel flip displays to indicate the words to be guessed.