I forgot to post at the time, but when in Edinburgh Airport on my way to Copenhagen I discovered a truly great piece of news: there is one more Terry Pratchett book that I have not read! It's a third short story collection, "Father Christmas' Fake Beard", collecting a few more of his early writings. That, alas, really will be the end, but never mind - it's one more bit of extra time I didn't know was coming.
#54: "Pathfinder: The Flooded Cathedral", by Mikko Kallio
#55: "SS-GB", by Len Deighton
#56: "Xanathar's Guide to Everything", by Wizards of the Coast