There's a 27th tribe. The Tribe of the Distant! -shameless plug-
Anyway, to actually answer your question... I think that what happens if a Tia splits off and forms their own tribe, it becomes somewhat of a sister tribe, not something completely different. So... let's say someone from the R tribe splits off, kay? Well... He and everyone who left are still part of the R tribe, they just started... their own R tribe, I guess. Now I could be completely wrong, but that's kind of how I took it.
Anyway, to actually answer your question... I think that what happens if a Tia splits off and forms their own tribe, it becomes somewhat of a sister tribe, not something completely different. So... let's say someone from the R tribe splits off, kay? Well... He and everyone who left are still part of the R tribe, they just started... their own R tribe, I guess. Now I could be completely wrong, but that's kind of how I took it.
