There was something I saw (and didn't see) in the last CSM codex that made me wonder if the fluff was being changed. As far as I knew, during the 13th Black Crusade Ahriman obtained an alliance with some Dark Eldar in order to access the Webway in his search for the Black Library, and the DE faction in general was somewhat neutral, using the confusion to gather slaves and wreak havoc. However, the new CSM codex makes no mention of Ahriman using DE aid, and in fact (iirc, I do not have the book right now) states that Dark Eldar actually fought against him alongside the craftworlders and the harlequin. So - did the Commorites switch sides when I wasn't looking, or am I missing something that explains it?
It is certainly possible that certain DE might have helped Ahriman, while others later fought against him, but there doesn't seem to be all that much on what they were doing - and you'd think a mention of Ahriman using the DE on his big project would merit a line in the CSM codex. Do you think this is a subtle change of fluff, or just stressing different parts of it? As a matter of fact, what sources exist on what the DE were doing during that time?