Have to remember that alot of the time Kaleuns didn't stick around to confirm kills,you dived into the cellar or you didn't live to tell anything at all,from alot of the books I've read,alot of kills claimed where when crews heard an eel explode at the end of its run and it was unsafe to go to periscope depth to check,it was just assumed that the eels had hit they're mark
If the U-boat surfaced later and saw oil on the surface and debris it could be rightly assumed that the ship went down,even when it had managed to limp off and keep up with the convoy
there are a few stories of ships being hit and carrying on and being sunk later with two different U-boats claming the kill!
in the end,in the heat of battle,accurate record keeping wasn't a top priority,and as someone rightly mentioned,propaganda was a very effective weapon
