Onetrack,
That's an interesting opinion piece regarding the pings. In line with that opinion, I would consider by far the most concerning angle, would have to be the inability of the Bluefin 21 to pick up consistent, repeated pings, once the pings had been recorded over a 2 hr period.
Just a minor correction to your post.
The Bluefin21 does not pick up 37.5 kHz acoustic pings its an Underwater Autonomous Vehicle with sonar mapping capability only. Unfortunately its operating limit 4500m depth maybe now of a concern, since nothing has been found.
The TPL-25 Towed Pinger Locator is what I think you are referring to.