I have one of those ... (and the game to go with it)

Red lamp boards definitely make those prototypes ... if they were never put in games, they were either mockups, or might have been use for fit-testing, etc.

Twilight Zone distributor aerial sign/display ...

tzsign_(resized).jpg

SafeCracker, with one of 9 prototype playfields (this is was the Engineering Sample), being played at SFGE 2016.

(Game won Best in Show, btw ... )

scsfge_(resized).jpg

And, regarding the blue powerball ... this is why you don't use one ...

23-blupb_(resized).jpg

There are some design differences on the playfield involving wiring (I had to change a number of plugs to match what the software thought was supposed to be where) ...

The rear saucer/upkicker (above the jets, for the roof entrance to the vault) on the prototype is a plastic saucer insert the ball sits on ... on production games, this is routed into the playfield wood.

The biggest difference is every single rollover switch on the prototype is a reed switch ... as a result, the game plays ungodly smooth and fast as lightning.

Some of the artwork is also different, mainly on the varitarget lamp inserts, and the drop target lamp inserts.

LTG - this was in reference to the Shadow mini playfields, each with two red lamp boards ... I'd almost guarantee those came out of the design labs, and not the production line.