Enma
draws Ryuo, i.e. Armament Haki.
Against Kaidou, we really only know Zoro used CoC because Kaidou sensed it.
It didn't have the visual markers of CoC, those appeared in the form of King of Hell when Zoro
fully awakened his Conqueror's Haki and mastered Enma. The blade has never fed off Zoro's Conqueror's Haki without his permission before or since.