Of the characters that seem apostle-like which seem like they are definitely apostles? Grunbeld is a no-brainer, Irvin(Arvin?) seems like a candidate. But Locus seems more like a regular human to me. Does it seem possible that Skullknight was once an apostle to anyone, I guess there are other ways to get that kind of power, but theoretically couldn't an apostle turn against their "masters?"