A radical distributionist can have good reasons for regarding many, if not all, prior claims or entitlements as illegitimate, quite apart from the fact that the badly-off have a stronger claim on the goods they need in order to reach the fulfilment as human beings to which they have the right. Flew himself makes a lot of the difference between resorting to compulsion and failing to do so. I take it that he will acknowledge that stealing is a way of resorting to compulsion. What has been gained through theft is illegitimately held. So is what has been secured through unjust war, murder, enslavement of other people.
Receivers are somehow or other thieves, too.
But then, most, if not all, current owners have an illegitimate claim to what they own. Money, Vespasian said, is odourless. I am quite sure no-one can be sure of that. Positive law may prosecute the direct receiver while letting alone the receiver's receiver and so on. Positive law still allows many unfair trade practices.