Perhaps I misled myself, because I noticed some "drive=0" tags in some of my /drive?/fids/*1 tag files.. any idea what those are for?

Um, my guess is that they're vestiges of a half-implemented feature, abandoned when we realised that nobody really needs to know which drive a fid is on. Sorry. ISTR there's even a drive column somewhere in Emplode, full of zeroes.

Peter