I'm using the BC files which you and I created between us, Jon, so I don't know why they vanished.
This book required a lot
of manual formatting (about 2h work after loading into BD), so forgive me if I'm reluctant to re-do it all
EDIT: I've just checked, and my BC files definitely do convert "--" to "uni(137)" which is the emdash, so it's a bit of a mystery.
I'm not too bothered - the books look OK to me.