Yes, coincidence. It was submitted for publication but rejected in 1863 (and then lost in a pile of papers and re-found in 1989). Anybody familiar with e.g. how most of Tolkien’s works were published posthumously won’t be surprised. Jules Verne wrote a lot, and he did not have a Christopher to comb through the boxes of papers he left. There are 200k pages of drafts, letters and manuscripts in a museum in Nantes, and not everything ended up there.

And I don’t see why the Internet is relevant: not everything that happened since the mid-1980s are internet-related conspiracies.

I read it, and my disappointment was immeasurable, and day ruined. The novel is just bad. It seems the real story is that it was a draft which J.Vernes and his publisher discarded exactly because it was below expected quality line, and not because "prophecy implausible". Fast forward to our times, and someone decided (not without a reason) that it's possible to sell anything with J.Vernes name on it, and marketed it as a "lost manuscript" accidentally found in "family safe".

Do you know if other of his works merit the sort of effort which has gone into re-translating and correcting _20,000 Leagues Under the Sea_?

I was very glad to re-read it when:

https://www.usni.org/press/books/20000-leagues-under-sea

was published.