Detecting when a player has completed an Emissary quest

[MuffinManKen]

I'm trying to detect when the player completes the objectives for an Emissary quest ("Complete 4 World Quests in Drustvar").

With Paragon reward quests I was able to detect that via QUEST_ACCEPTED, but with Emissary quests you actually accept it as soon as the Emissary is available on the World Map.

So I tried QUEST_WATCH_UPDATE and then check if there are no incomplete objectives, but at the time of that event the update hasn't necessarily happened.

Is there an event I can listen to that will do what I need, or do I need to mess around with timers so I can catch delayed updates?