At the point he is universally recognized like Calzaghe was. He beat a titleholder to earn it not a champion unless you think Kessler foguht Sartison for all the marbles.
Well, this is ESB. You know there are lots of definitions floating around. Some have said that if you beat a champ, paper or not, that is good enough to lose the paper designation.
It's all relative and comes down to everybody's opinion. Technically yes but you can beat a complete bum for the interim champion in recess title while another good guy fights another good guy for a vacant interim title yet that won't receive credit which is weird to me. The fighter makes the belt and can legitimize the paper championship. That being said I hgaven't done a study but prolly over 80% of champions today are paper champions so like I said it's all relative. To me you can't be called ''champion'' until you are recognized by all. Till then you are a beltholder altough technically you are a world champ.