I believe that Bill's event that you describe was actually during the recovery from an intentional spin, not a loop
Hi
LOMCEVAK, all the references I've seen say loop when demonstrating the aircraft to the Swiss, during one course the event was used as an example of the effects of DA on performance, and as an example of even the best are capably of screwing the pooch without any help. The spin event was another item on Bill's CV.