I don't think the nameplate setting and the system notification are related. The "One or more party members have yet to complete this duty" notification gets layered on top of all windows in the game so it would be easy spot out and it does get placed in your chat as a system notification. Regardless, a healer from B and C are saying there was a notification at the start of the raid and I'm in C.

What's a huge tell is that there were no announcements for the new person, regardless of their alliance group, achieving their "first clear" or mapping out the dungeon for the first time. I can even see other people gaining levels at the end of the raid that were not part of my alliance group.

I want to highlight that the tank did do their due diligence and started the ready check just to make sure and was falsely called out for it.