What tripped me up was the seemingly-conflicting notion in the post that, typically, salvage belongs to the salvager, not the owner. It seems like the opposite is true? How it read to me was that there must be some kind of exception for insurers once they take ownership of something, but if the default is actually that the owner still owns it (minus reasonable salvage fees, and if they can prove it) and the point was that it was impressive they could still prove it after all that time, then it all makes sense.

That’s not what is happening, or what salvage means?

if there is no identifiable owner, then the salvor (the one who salvages) is generally entitled to the property as a reward for salvage, but not always. [https://en.m.wikipedia.org/wiki/Law_of_salvage]

If there IS an identifiable owner, the salvor is entitled to a reward that takes into account the difficulty in salvaging and the value of the salvaged property, assuming there was no contract that was more specific.