So I haven't read his origin or any of his major comic stories yet, but from what I understand, his comics origin is kind of his movie one turned inside out - he was born and grew up in Wakanda, where he was N'Jadaka, but when he was still a kid his family was exiled for reasons that don't need exploring etc., and they were forced to survive outside, and he swore revenge on the kingdom for kind of understandable reasons, and at some point he renounced his Wakandan name and chose the name "Erik Killmonger" as his supervillain name. Because in 70s comics that's what you do. So using "Erik Killmonger" as his AO3 tag for the comics version kind of makes sense; it's the name he uses by choice for most of his canon. I don't know if "Erik Stevens" has any comics basis -maybe he used it between leaving Wakanda and becoming a supervillain, when he was at MIT?

In movieverse he says outright that Killmonger isn't his name; it's a nickname that was imposed on him by the colonizers and you get the impression he doesn't really like it; and you get the impression he's been thinking of himself as Prince N'Jadaka most of his life even if he couldn't use it outside his family. I would be okay with piping "Erik Stevens" even, or some combination of the three, but right now the tag is just Erik Killmonger, which really doesn't seem to work for movie canon. (Does he even ever go by "Erik Killmonger" in the movie? He's credited that way, but if he uses it it's only when he's undercover with Klaue. And I get the impression that if T'Challa ever called him that really bad things would happen right after.)