Quote Originally Posted by JowyAtreides View Post
In the unlucky event that you're looking for an npc that gives cards you already have, you'll just have to root through them all
I think they still have the new duelist mark on them, even if you got the cards they drop from different means. But your idea would be their best bet, imo. I'm currently using the https://triad.raelys.com/ site, since ffxivtriad is ded. Cycling through all the duelists, while tedious, is one way to check what's missing.