At the time, I was kind of critical of Priest and Marvel editorial for pushing the "never been defeated" narrative despite this issue existing, and for offering no explanation of Killmonger's resurrection and what happened to him afterwards.
Well, while I am still miffed by the "never been defeated" thing, I was wrong about the latter. It was mentioned, I just didn't catch it when I read it.
It was right there, hiding in plain sight the entire time. I guess since I had no idea Over the Edge existed, I just glossed over the very, very obvious explanation given and the very, very obvious citation.
Priest is a God, I am merely a mortal trying to take it all in.
I updated the Round 3 of T'challa vs Killmonger to reflect this discovery.