It seems that Skullknight has a good number of behelits in his possession, or in his belly. I would assume that he has slain a large number of apostles in the process, but we don't seem to see Skullknight actively battling apostles. That could just be a result of how Miura is presenting the story of Berserk, or maybe Skullknight doesn't sully his hands anymore. Or maybe he isn't allowed to intervene? Although he has in the case of Guts. If he has been battling apostles for this long, almost 1000 years if he is Gaeseric, I would expect there to be fewer apostles. Or maybe Skullknight didn't begin hunting until recently?