Former sub guy here. Finding an actively pinging device in an ocean would reveal nothing about a country's sub capabilities. It's a problem of big ocean, little ping. Accounting for thermal layers that distort sound and local conditions, it could be heard anywhere from a mile to 100 miles away.
I remember once we were operating near xxxxxxx, just xxxxxxxx ops. We heard a noise in the xxxxxxxx dB range, but it had a xxxxxxx hearing rate. It was new so we called it in. Turned out to be another boat near xxxxxx, xxxxxx miles away! Another time we heard a xxxxxxxx dB noise with a xxxxxxx bearing rate and it was xxxxxx miles away!
I think you can see that the answer depends a lot on ocean conditions more than sub capabilities. Nobody is going to to withhold information about this because they're afraid of disclosing capabilities.
I was talking about the big splash if it hit in mostly one piece, more than the silly black box clappers.
And the comment was more about who heard it and whether they were close enough to or not. There's of course, fixed listening assets besides the mobile ones, too.
If you think a government wouldn't sit on where they heard something odd, to obfuscate what heard it and where it was when it heard it... Right. Sure. Whatever.
We knew Kursk was down as soon as her owners did in 2000. We didn't make the first phone call announcing it to the media.
Won't matter if someone does know where it splashed or not. If they don't want us to know, we won't be seeing it on the news.
If one ship from Woods Hole has a "miraculous" find towing a sled, and just happens to sail to within a "reasonable search time" of where the airplane is eventually found, it'll just be a sign of the usual "intelligence" shenanigans.
Not that I care.
Hell, we built and sailed Glomar Explorer, from the open dock, right straight to a Russian sub, and attempted to hoist it aboard, pretending it was looking for energy resources.
And we tapped Russian undersea telephony cables with subs and divers.
Secrets and lies are child's play to the naval intelligence community. That's just par for the course.
Pretending we didn't hear or see something that we did, if those in power believe it serves our best interests to shut up, isn't that big a leap of logic at all.
Even admitting we heard nothing, leaks ancillary information that can be assumed/inferred, once she's found.