If I purchased legal downloads online, my name & the company's name is on the receipt. I also keep the PayPal receipt (if I paid using their service) and have my bank records to prove I made the purchase. It isn't too difficult to contact the company and confirm the purchase.
True but I'm speaking strickly of physical CDG discs now.... but on the subject of downloads I bet you'd be hard pressed to prove ownership on the spot... granted you could if forced to by court of law...
But when talking about physical CDG's if the disc is completly missing having a reciept and or cd insert, while it does prove you did own the disc at one time doesn't mean you still do... that's what I'm driving at.