Believe it or not, I know this answer. In fact, there are a few of us here at Riot do know the answer to this. That means that there many other at Riot that don't know the answer. Rather than be a DB and say "I know and I won't tell, ha ha," I'll tell you the reason why I won't give you a straight answer.
This question - and a handful of others I've heard on the forums that we've either given ambiguous answers to or just completely dodged - fall into a category known as a "bible point". Bible points (others call them by differing names) are key story points that define help the rules of an intellectual property. Bible points are basically unexposed spoilers. They are rules that seem mysterious and often times contradictory to the rules of the world. There shouldn't be two of the same person in a single battle arena, should they? It doesn't make sense that it happens... but it does.
To outright spill the beans on something like this sells short potential story development we are basing on this bible point. Yes - we have some story development in store that specifically addresses this issue. It may or may not answer the question when it fully plays out. (Spoiler - part of it involved a forthcoming champion.) Still, we recognize that this is a key bible point and we want to do something substantially creative with it.
I'll try and do you one better... Over the weekend (I'm trying to get home right now but I can't tear myself away from this thread~) I'll try to spin you a little ditty that somewhat deals with this issue. I've wanted to do something on this creatively for some time now, outside of what we have planned. There always seems to be a priority that comes up that tears me away from fun writing. I'm going to keep it under 1000 words if I can, provided nothing blows up on me this weekend!