I'm glad you mentioned that. It's pretty much what I recalled, too: learning a level of one "reduced" the maximum level you could learn of the other (ex: A Solar with a Shadowlands initiation could gain a Terrestrial and Celestial initiation, but not a Solar one) .
I went poking around for more information. The discussion in this thread suggests that's just a holdover from first edition, put into the main book's lexicon before they'd actually gotten the rules down for necromancy. If that's right, then there's no problem with Misho having mastered the Adamant circle of sorcery, and up to the Labyrinth circle of necromancy.
EDIT: And ninja'd by Kyeudo the Swift.
DOUBLE EDIT: Who came pre-ninja'd by Jukashi himself. ^_^o
Though it should be pointed out that Jukashi suggested Misho still has his old initiations kicking around. Mentioned in the blurb for this comic:
Originally Posted by Jukashi