Hey Boswell
Never worked Crepe before but from just looking at it, A is the bark, B is the inner bark (or liber, or phloem) which is prolly pretty soft and needs to be removed. Should go down to C for the whole back of the bow although just to the right of C on your pic it seems like you already went down to a lower growth ring. If so, you should chase that lower ring for the whole back, being careful not to cut down further. I have no idea if 56'' is pushing it for crepe at 27'', I'll let more knowledgeable folks steer you for that one.
Cheers!