That's the key, though... KNOWINGLY stolen! If you purchased an item but where unaware that it was stolen, there's no legal issue and, unless there's something that can link that item back to it's original owner... I guess it's yours then.

As far as the digital key is concerned, this is even more nebulous. Sure, their database or software thinks the key is stolen, but that's just a binary bit somewhere which could, by accident or by a bug in the software, be in error. If, as a purchaser, you were unaware that the dealer from which you purchased said key was selling keys illegally, they is the same as buying a stolen TV from the flea market. Unless you knew, you did nothing wrong. As for the software telling you it's stolen... again, that's only what the software things. It could be wrong.

Additionally, purchasing suspect keys is even more legal as there's no intrinsic value to the key itself. It's just a string of numbers and symbols. Keep it, it's yours. Have fun. Play hangman. The company who owns the software for which that key was intended... didn't loose anything. They still have their software. If the key worked? Well, if the key worked, that means the company and/or software doesn't think the key stolen or otherwise illegitimate (which, can also be an error on the companies part).

In this case, the company says, in essence, "We think this key is stolen, but we cannot prove you did the stealing. We're not going to belabor the issue. Keep on, and let your conscience guide you"

Sounds like that may rankle your sense of right and wrong, but, them's the fact. You have never seen someone arrested for purchasing a software key, nor have you seen anyone arrested for purchasing a physical product they believed to be legit even when it wasn't.