Apologies if I’m going over old ground here, but I’ve been away from the forums for ages, and can’t possibly catch up on all the threads.
Anyway, what’s exercising me is, who destroyed Erf? Here’s an idea, which ties into the search for Earth and what the relationship is between Earth and Erf.
Maybe the 13th tribe set out to look for Earth, didn’t find it or found it occupied, for example by our descendants who were also the ancestors of the humans who originally colonised Kobol (so BSG is set in the far future of our universe). So, they settled on a planet in a nearby system. However, the 13th tribe of cylons on Erf had problems with the humans on Earth (our descendants) and there was a war. The humans from Earth wiped out the Cylons of Erf, mirroring what happened between the cylons and the colonials.
This idea has a delightful symmetry, and also explains Anders’ (or was it Ellen’s?) comment that human-cylon separation doesn’t work - they have to merge or be continually at war.
It also means the newly combined cylon-human fleet can still find Earth.