I was figuring that a minimum of 10 spells would create a Class Spell list. Now, one or two of these spells might already be on the already existing spell lists for a given School of Magic, but certainly not all of them (however, once I create the Class spell lists, all of those spells will be available to Minor and Major Adepts of the same School). I am planning on creating new spells for each Semi Adept Class...
Think of it like squares and rectangles. Squares are the spells of the Class Spell Lists, while Rectangles are the spells for a school of magic. Thus, just like "every square is a rectangle, but not every rectangle is a square", we have all spells from a Class Spell List are part of a School of Magic, but not all spells in a School of Magic will belong to a Class Spell List.
