We have a notable point where Sev'rance is described as the 'leader' of the Dark Acolytes and we then see her replaced by Ventress, who herself becomes Dooku's secret apprentice and very prominent herself. Are we to assume Sev'rance, due to her prominence, as head of the Dark Acolytes, as Supreme Commander of the Separatist armies, is just as important to Dooku? He would have had her to hand for the last two years before Geonosis, and he tasked her with securing his own escape route during the battle. Seems likely to me, but also mere speculation on my part. Of course, we then have the question of who Dooku's apprentice was after Ventress, though potentially his play of Sora Bulq and Quinlan Vos against each other (as his last Acolytes), could be interpreted to be him selecting an apprentice, as much as Vader planned to do with Lumiya and Flint... thoughts?