How did I start this thread?
FWIW, after those posts I've looked into it a little further, and there were several instances where JANAC gave credit for small freighters sunk that the sub did not claim. One of Tang's patrols featured this occurring, among some others.
It's very possible, even likely I suppose, that many of these unclaimed confirmed sinkings were the result of unexploded torpedos punching holes in a ship.