It could exist, or perhaps those are just mockups used for promotion. Or perhaps the build that is represented was overwritten or destroyed. However, all it takes is one person to put it up for sale one day. The Famicom version of Monster Party was long assumed to be the stuff of legend, but out of the blue, around 20 years after it was made, a prototype of said version shows up for sale. And, given the somewhat professional appearance of the cart, there could very well be even more copies of said game out there waiting to be sold in the coming years. Not every proto owner posts on game forums, and some are not even gamers, or at least don't realize the value of some old cart with a shoddy label that they found at a flea market or was given to them by a friend. Not everyone is intentionally hoarding games, and even if they are, they don't have a duty to share anything.
Prototypes for old games show up for sale very regularly, even obscure ones, popular ones, or ones that differ notably from the final release, so just keep looking and who knows, somebody might toss one up for sale.
The real question is, are you willing to spend the couple hundred that it could fetch at auction?
Edited: 02/02/2014
at 04:52 PM
by CD2193