Well... that is the difference between PR and practicality. PR says "can" like they do it every day.
While they could run prototype boards down the line, it is not quite as easy as the video makes it sound and it is unlikely they would do that lightly.
To run a prototype board down the line they would have to:
* Get the prototype PCBs fabricated (in 1990, this took a lot more time than today where you can get a multi-layer board fabbed in days). Note also that the NeXT boards were probably a lot more than 4 layers, which adds time and expense, especially 20 years ago. The good news is all the other items probably would take less time to complete than the PCB fab, so this would be the pacing item for the schedule.
* Get a new soldermask made to match the board.
* Procure the necessary non-production parts. With luck, can get small quantities (or samples) quickly from distributors.
* Reprogram the pick-n-place machines to put the parts in the right places.
* Load the pick-n-place machines with the right (new non-production) parts.
* Possibly have to tune the soldering ovens to get the temperature/time profile right (should be OK for small part changes).
Once everything is in-house and programmed, you can simply queue it and it is done.
It's also likely that they did it on the same line because the automated equipment to build the stuff was so hideously expensive that they had to build it on the same line.
While they could run prototype boards down the line, it is not quite as easy as the video makes it sound and it is unlikely they would do that lightly.
To run a prototype board down the line they would have to:
* Get the prototype PCBs fabricated (in 1990, this took a lot more time than today where you can get a multi-layer board fabbed in days). Note also that the NeXT boards were probably a lot more than 4 layers, which adds time and expense, especially 20 years ago. The good news is all the other items probably would take less time to complete than the PCB fab, so this would be the pacing item for the schedule.
* Get a new soldermask made to match the board.
* Procure the necessary non-production parts. With luck, can get small quantities (or samples) quickly from distributors.
* Reprogram the pick-n-place machines to put the parts in the right places.
* Load the pick-n-place machines with the right (new non-production) parts.
* Possibly have to tune the soldering ovens to get the temperature/time profile right (should be OK for small part changes).
Once everything is in-house and programmed, you can simply queue it and it is done.