User blog comment:LordRimus/Ranked magic/@comment-27137888-20151108210638/@comment-27036174-20151110200524

What Rimus means I think is that Ainz can learn more spells allowed by his classes. He isn't saying that Ainz can gain new classes and therefore levels. For example let's say that a class that he has allows for you to choose a spell to learn from a pool of ten possible spells. Ainz's dark wisdom skill would allow him to choose more than one spell from that class to learn, thus making it possible for him to learn more spells, but not spells that are not allowed by the classes he has.