From Ken Fedesna who was head of engineering and modern days with Team Play-
As Larry has already replied, the "XP" was reserved for the early prototype cabinets. Also as Larry has stated, the art would sometimes change between prototype, sample, and production runs. What is unusual about this though is that it is numbered "63" which would probably indicate that it was a "production sample" and not one of the first "prototype" cabinets. We would first put together a very limited number of "prototypes" for testing locally, then manufacture a limited number of "samples" to send out to distribution and solicit production orders , and then start actual "production". The "XP " was usually reserved for the "prototypes, but we would normally only build 10 to 15 "prototypes. The number "63" would seem to indicate that this was the 63rd game built which would make it one of the "sample" units. I will check my records and notes from back then to see if I have anything more, but I highly doubt that I have anything with such "details".
Ken