well lets look at the evidence. one point you bring up is the top of the cart
this is the best look available from the auction pictures the Shreddin' doesn't really look printed but written
you will also notice that the fade pattern and burn into the plastic this game spent a really long time in one place under harsh lighting conditions in a cart case and going by this picture the case was backwards.
now onto the manual the manual is NES-WV-USA *(same on standard manual) looking at a standard manual you will notice some differences one is the lack of the color the other is the staples. to me this looks like a photo copy of a regular manual the staples being uneven indicate it being a manual stapling probably with a standard office stapler. this practice was common in the rental field.
while there have been protos with finished artwork that is not a common thing they usually have any type of white label on it be it some type of dot matrix printed label or even some VHS labels to hand written, then there are some with other game labels on it, but they usually have cut outs for the larger chips.
what i see with this game is a rental with an upside down label that spent a long time on the shelf in a rental store in a backwards case. so as far as a proto i think you dodged a bullet, but i will be using a pic for my site