So, I've completed the books that I want to read from Terry Pratchett that are not part of the Discworld series. Pretty much the only ones I've left out are The Carpet People and the Bromeliad Saga.
I've really enjoyed the Johnny Maxwell trilogy.
Nation is a fun story of south Pacific natives and a European shipwreck after a tsunami from a volcanic eruption. And that's not completely redundant.
Dodger is a great historical fiction set in London before Charles Dickens has begun writing his fiction.
I only realized from this reading that The Dark Side of the Sun and Strata may be written in the same science fiction universe. I can only imagine what Pratchett could have done as an author if he had decided to write his satire in an arcing sci-fi story instead of fantasy.
And now I have the 40 books of Discworld to look forward to, as well as several short stories, and addendum books. Perhaps before I finish the series, Pratchett's final book (a fifth story of Tiffany Aching) will be released.