So I've read all of the Secret History (except for the new Compendium of Srem), most of the old editions, and most of the new editions. One thing that confuses me is that the conflict, in the original version of the Keep, is described using the terms Chaos and Light. In the RJ series, and in the revised Nightworld, it is described using the terms Otherness and Ally. Were the terms changed during the revised writings? Is there a revised version of the Keep that uses the terms Otherness and Ally? Are both terms meant to be used?

Chaos was the archaic term for the Otherness (see "Demonsong"). As time went on and people came to realize that chaos is the quotidian state of reality, the terminology evolved. (How's that for fudging off the top of my head?)