Haha, yes - I'm glad someone mentioned the letters! Don't feel bad though - even my beta asked me what the salutations and conclusions of "LB" and "BB" were supposed to mean (Little Brother & Big Brother, for Sirius & Regulus), so you're definitely not the only one, and it was meant to be a figure-it-out-as-you-go sort of thing. =)
Anyway, thanks so much for the lovely comment (and for spending your afternoon reading it, lol)!