I have lots of experience with single lung + one other organ hits(usually liver) if you give them time the other organ will catch up and you' ll have a dead deer to find fairly easy. I have one experience with a single lung only hit. It was on a doe that moved upon release and I hit the shoulder bone at a funny angle and got next to no penetration. I waited an hour and got down to investigate. Very shortly I found bubbly blood I took up the trail and followed it a good ways past another hunter who saw my deer limping, with its head down. He said it bedded down just out of sight. It was then I made the decision to stay on the deer. We jumped the deer and noticed it struggling to move, so I stayed right after her. She ran maybe another 75 yds from this point before collapsing. I agree that at certain times it is a call to be made right then, and something not really planned for. In my situation I believe I' d have found the deer either way.