No, the sources are horrible. You can easily fake up any number of Bob Rosses and simply say, "ah yes, I discovered another one of the tens of thousands of Bob Rosses which he sold as a young man or whipped out in a charity event in a small podunk place, and the original owners prefer anonymity". In terms of provenance, the sheer number, blandness, and indiscriminate original distribution of paintings makes it sound like a nightmare. If the market were more developed, so selling Rosses wasn't so unusual, I bet forgery would become a much bigger problem (although you wouldn't be able to tell if done somewhat competently - how hard would it be to get paintings and canvases from the '80s and defeat pretty much every possible forensics? that was not long ago at all... We're not talking trying to forge Renaissance masters here.)