There's probably a simpler reason.
Based on Emet's reference to the volcano when Venat asks how Azem has been doing, Elidibus is already Emissary at this point. I have a question, though.

Would you wear the red mask even if you wanted to travel around incognito? I'd be surprised if they let Emissaries go off on their own to explore spooky castles with dread slumbering beasts within. This seems a bit like trying to sneak into to a dungeon with a crown on your head.