From 4 years ago.

Tiger, could you explain further please. First I've heard of that. Thanks

Pinball Database says 191 we made. The original number to be made and pre-sold was lower than that. But Gene had left over parts at the end so he made the EXP numbered games and sold them. I think it stood for Experimental for some reason. ** Corrected below, stands for Extra Parts.

Serial numbers are impression stamped on the cabinet, cabinet head and the front edge of the playfield. The EXP game serial numbers began with EXP followed by the number.

The pictures I've attached are from my prototype, Illinois Pinball BBB. Prototype serial numbers began with a "0" and I had #013 of 19 prototypes.
Regular production games began with the number "1".

More pictures of the protype are on the database under my name.

On the playfield edge picture, disregard the ink stamp to find the impression stamp.

image-B22 (resized).jpgimage-B23 (resized).jpgjimage-34 (resized).jpg

Yes, correct. Thanks Larry

Not sure about the EXP games but everybody got the brass plate insert card and the ability to have it inscribe however they wanted.
Because my game was #13 and I am not superstitious at all, I named my game Superstitious and I surrounded the word with 13 question marks.