My theory is that as long as the fourth wall is active MC can never become a true "character" in this story even after he reaches the end of the novel story line, but whenever he becomes too immersed or the ability weakens he does become a character temporarily. So far, the status of characters like Gilyeong and Sangah seems more interesting to me, since they aren't treated as "characters" either.
Also I like the historical tidbits.