Didn't one get killed when they were sharding the others?
Well, if it's about material victory then Chaos shouldn't really be considered. A) Because the Chaos Gods themselves aren't really a player in the material realm, and have shown themselves to be largely uninterested in it. B) Because the Chaos Gods aren't in a mutually exclusive situation with everyone else: they can 'win' even if another faction wins complete control of the material realm. C) Because the Chaos Gods can't loose. Without a definitive loss state it's hard to say what a definitive win looks like.
One c'tan, yes. A fluke that has not been repeated since and had a devastating consequence.
To your second point, I originally referred to Chaos in general, meaning daemons and followers as well. The c'tan I referred to separate to the necrpns because they are no longer technically on the same side by choice.