The small overlap test might've been not conducted on the Prius v wagon when you bought.I can't wait to sell our Prius V. Yes, we get 47 mpg and can carry lots of stuff ...but I would have never bought it if I first watched the crash tests.
IIHS seems to have the habit of moving the goal posts and then liking to broadcast that Toyota didn't do well on these new goals: IIHS rating on 'small overlap front' test crash | Page 3 | PriusChat.
All vehicles are optimized for known crash tests for their market (e.g. NHTSA full frontal, IIHS moderate overlap/offset, Euro NCAP, etc.). When you introduce a new test that few or none are optimized for that's much harder on a vehicle since the force is over a smaller area, of course most not optimized for this unknown at the time of design finalization won't do well.