It seems to me from the initial topic and that quote alone that you're not entirely convinced.
I do trust the butcher or I would have taken them elsewhere, it's the weight loss which I found hard to accept, that's why I asked for your opinions and it seems unanimous that the weight is pretty much what it should be at 80% of dressed carcase weight.
You're missing neck on that list? You should have had that back. The breast if it's been rolled I'm sure would have had some deboning, have you tried rolling a breast that's boned 
Yes the neck was missing and the breast was rolled with the lower part of the ribs still intact, more of a 'slow roast for casserole' joint.
Maybe best to learn how to butcher your animals yourself.
As I posted previously, I normally butcher my own lambs, but time is not on my side at the moment. However I've never weighed the carcase or the butchered joints before, hence why I asked for your advice.