Thanks TuggyNE. I freely admit that the analogy to legal principles is partly b/c that's what I'm familiar with. The other analogy I've seen used is to computer code. The law one seems truer to life, to me, though, b/c RPG rules have to be used and interpreted by people in a way that computer code does not.
@SorO
I don't really follow the comments regarding Extra Spell, but that's neither here nor there. I don't really want to get too distracted by a discussion of precedent, it'd take us too far afield. Farther than we already are.
What strikes me as interesting here is whether citations to sources outside the rulebooks themselves add anything to a question about a rule. I happen to find "rule A is better than rule B" a sufficient, and stronger, argument than the resort of an FAQ or game designer for authority. But, this may be due to my general lack of faith in RPG designers combined with a sense that I know what will work at my tables better than they do. Also, it's an argument by authority, and that's generally not great.
Making the analogy to legislative history also makes me think that the hierarchy at play -- Game Designer > FAQ > random forum posts -- is not entirely obvious. For example, there's a series of persuasive arguments that if Senator X voted to pass a given law, or even authored it, later statements she makes about the law are irrelevant. Some of these would be relevant in the RPG design context, such as the idea that a given book is a collaborative work, so the final product is not just what Senator X (modulo Game Designer X) alone feels about it, but what the committee X, Y, and Z working together agreed upon. Which is to say that X's statements about the product aren't even authoritative.
The response, I think, and it might be a good one, is that the FAQ could have real expertise. If they sit around all day and kick the tires on rules, then presumably they are really good at thinking about them and how they fit together in a coherent whole. Something that even the game designers might not be doing. When you are creating a new rule you're not (arguably) seeing how it operates "in the wild."