>>12144291
There's basically only two plausible places where this game could come from, in my opinion.

The first is that someone at Namco had access to the game, and decided that he was simply gonna dump and release it because he was probably a fan of the series himself, and he wanted other fans to get a chance to play it too. He may be risking his job and possibly even litigation if found out, so for his own sake I hope he stays in the shadows.
OP could outright just be an intermediary for that person for all we know.

The second is the way that old prototypes otherwise tend to get out into the wild. Someone who had access to the game, be that a former employee, a journalist provided the game as a sample, or maybe some of the distributors actually DID get a copy it, and they just never returned it.
Then they held on to it, and one way or another (possibly their death, like their kids cleaning out their stuff and opting to just sell stuff like this), it probably changed hands to a collector or someone who seeks out these kinds of things, who himself either decided he was going to provide it for the world, or he himself passed on and whoever got it next did so.