most people don't put their name on it unless its a winner, so if its blank the only way to prove who bought it is perhaps if they have a till receipt with an exact time that matched the lottery machine, that states a ticket was purchased.
chances of finding that though are slim.
i would not give it a thought, i'd keep it.
although if i had lost it and knew it was a winner and had a itemised till receipt, i would make a claim as they can verify it on the main system. worth a try