Dogshooter,
I've seen a few caught by animals, but mostly by animals bigger than deer. Have a couple from gemsbok, which weigh 400-500 pounds and are built VERY soldily, with inch-thick skin on their front end.
And all the BT's retrieved from seer-sized animals were from angling shots, usually involving bone. Shot a Montana whitetail doe last year with a 100-grain BT from a .257 Roberts. She was quartering to me at about 50 yards, so I aimed right for the near shoulder joint and hit it. Found the bullet under the hide at the rear of the ribs on the far side.