It really doesn't matter if there is a stitch of documentation or proof supplied... luch is right, condition is king... and it looks to be in spectacular shape! GLWS.
Agreed, if I ever sell anything, doubtful I would even remember when I purchased the thing, let alone having documentation going back decades. Plus, when buying a game, at the time you ARE trusting the seller about the provenance or issues. Sometimes, who previously owned a game is not that clear.
What
@luch said, condition is king! Nothing beats looking at a game yourself, playing a few and making sure everything is Ok!
Or, in my case (it has happened a few times), buy from someone you know or someone that has references from people you trust. It's not that big of a hobby, people get to know one another.
Lastly, a fantastic looking game may still have some issues after the sale has occurred, sometimes transportation does that or maybe the original owner never saw it. But there's enough folks with abilities, there's enough parts, to fix things and make a game solid for the next 20 years!