It's an educated assumption, though. The only game I know of that is big enough to have had that problem is hattrick and that's how they do it.

As for who gets in? TD, II, III...etc until you can't put an entire level in. Then that division gets split up by rankings if we have them by that point or just put in randomly.

This is all hypothetical, though, as GI will never get that large. Again, I'm assuming that GI will never be that large, but I'm right, so that's ok.