From the Cook/Marsh (B/X) Expert set:
Magic-users and elves are limited to the number of spells they may know, and their books will contain spells equal to the number and level of spells the caster can use in a single day (thus, the books of a 4th level elf will contain two first and two second level spells).
Most player character magic-users and elves are assumed to be members of the local Magic-Users Guild or apprenticed to a higher level NPC. When player characters gain a level of experience, they will return to their masters and be out of play for one "game-week" while they are learning their new spells.
(page X11, emphasis added by me)
Magic-users may add more spells to their spell books through spell research.
Spell Research. New spells may be researched by any spell caster. Research requires both money and time spent out of the campaign.
Upon reaching 11th level, a magic-user may choose to build a tower...a mgic-user who constructs a tower will gain 1-6 apprentices of levels 1-3.
(page X7-X8; again, emphasis added by me)
Based on the text of the game, I am revising the acquisition of magic-user and elf spells in my B/X game. In reviewing the rules, I've decided on the following interpretation (and not without a bit of internal debate):
- Magic-users and elves may know a maximum number of spells (that is, they may have a maximum number of spells in their spell book) equal to the number of spells they can cast per day. Why they can't "store up" extra spells or rob spells from other magician's tomes is a mystery that one can interpret in a variety of ways (and I'm not going to make something up right now). While this is a change from how I was running the game earlier (I was allowing spell research to "add extra spells" to the spell book), I feel this is the correct call for the sake of game balance. Even AD&D limits the maximum number of spells available to PCs based on Intelligence, so I don't feel bad in limiting the maximum number of spells that can be known...though I'm guessing this won't sit well with my players.
- Magic-users and elves learn their new spells for "free" so long as they are apprenticed to a higher mage. I am tempted to cut players off at 4th level, for a couple/few different reasons: A) the wizard in his tower attracts apprentices of levels 1-3 (which can be interpreted as levels 1-3 being the collective "apprentice levels"), B) 4th level is what I consider "hero level" for most classes based on the break point it provides for most B/X classes and the fact that it is the 1st level of "Expert" play (levels 4-14), C) I've seen 4th level as a cut-off in other places as well, notably Dragon Lance (where magic-users were expected to take their Test of High Sorcery at level 4). Also, at higher levels elves and magic-users start to gain more than 1 spell per level, making that "week off to get spells" rule especially kind.
- A magic-user or elf who is NOT apprenticed may only add spells to his spell book through spell research. There is no minimum level for spell research (unlike magic item construction).
All right, that's it...and that's probably enough for now. Here are a couple different ideas I'm consiering adding that AREN'T based on the rules of the game:
1) Bonus spells for magic-users/elves based on their Intelligence score (sorry, no bonus for clerics/Wisdom).
2) Toying with the idea of a "graduation test" to level up beyond "apprentice stage" (like the Test from Dragon Lance).