You don't have to do that manually, if there are free butcher stations and free labor to do it they'll go handle it automatically (at least if the (o)rders option is set iirc).
Right, yes. I've fiddled with the defaults so much I'd forgotten that detail. I was sick of my dwarves interfering with time-critical slaughter tasks by picking up yet another forgotten beast corpse, and/or running into danger to grab still more corpses, and had turned it off.
Auto-butcher is on by default.
Odd. I've had my guys end up using goblin bones to make some items (Unmodded), so how did I end up with those?
A severed head will decay down to a usable skull and severed limbs of appropriate size can decay to a single bone, which is how I've wound up with the bones of goblins or other sapients turned into bolts.
I'm guessing these go together. Still, I thought I read somewhere that dwarves wouldn't use bones even then. Hmm.
I've had stuff made of goblin bone as well, crossbows and totems and stuff, although I'm not exactly sure of the process that was followed to obtain bone from mashed up corpses. I do know that after a big wave of invaders come through, a lot of the corpses need butchering, although I don't pay too much attention to exactly what kind of corpses - I just build a bunch of butcher shops down by my refuse pile and let the butcher crews handle what they want to handle. I play with the Fortress Defense mod so I always have a pretty huge variety of corpses, many of which are non-people (animal mounts e.g.).
And I'm
guessing that this is a detail in that mod. I haven't used it. Or, well, the above decay explanation could come into play, since you have so many corpses total to handle that they sit and wait.
Someone with more knowledge here could be helpful . . .
--Rexfelum