I may be able to solve this riddle with some 'nerd' knowledge. The Total Codex predicts the fates of men. Soulblighter did not need to know about the Summoner, because he is a part of the man's fate. So, theoretically, he was supposed to meet Soulblighter and nothing could have changed that. Explaining the whole fate thing is hard to do. I hope you get the general idea though.
Soulblighter doesn't need the Codex to know about the Summoner becase;
a). He already knew
b). It was 'written' in his fate that he would meet him.
