So, as of today we have a new national holiday: Juneteenth.
This celebrates an event that I first learned about by a circuitous path.
Back when I was doing some research into unfinished novels where the author had produced too much material, not to little -- like DOCTOR GRIMSHAW'S SECRET and of course THE SILMARILLION* -- I was intrigued to find that Ralph Ellison, about whose work I knew (and know) very little, after his death in 1994 had left behind a two thousand page draft from which was extracted a 368 page novel called JUNETEENTH (2000).
But as is sometimes the case with posthumously published work, there was criticism of the edited version, and it was replaced a decade later by a much longer, fuller text: THREE DAYS BEORE THE SHOOTING (2010). Being in doubt about which of these two published versions I shd read (because I didn't want to read both) I've wound up reading neither, though I have dipped into the later text and found it uncongenial.
It was thus by a roundabout way of trying to find out about a novel constructed from remains left behind by an author with writer's block, as a way to better understand JRRT, that I learned about the historical event celebrated in our new holiday.
--current reading: "The Lost Letter", my 2014 piece suggesting a new way to read Charles Williams.
*This also forms the core plot of WONDER BOYS, both the film and novel versions.
Capote's ANSWERED PRAYERS is a good example of the more usual case, where the author claims to have written far more than is found to actually exist after his death. Which, come to think of it, is also like Tolkien.