I've had them for at least 25 years....
Just off the top of my head, others that I've had about as long or longer:
Mervyn Peake: Gormanghast
John Crowley: Little, Big, Beasts, Engine Summer; Aegypt
Ursula K. Le Guin: Compass Rose
Peter Straub: Shadowland
Stephen King: Firestarter; The Dead Zone
Robert Aickman: Cold Hand in Mine; Painted Devils
Algis Budrys: Who?; Rogue Moon
Russell Kirk: The Princess of All Lands
Basil Copper: Necropolis
Walter de la Mare: The Best of ...
....And I know darn well I could triple or quadruple the size of this list if I were home.
I hope you will add to it, because several of the things you list above are ones I find intriguing, notably the two Budrys books -- unquestionably among my favorite sf.
I interviewed Kirk about his ghost stories in the mid-1980s. The interview was conducted in a restaurant in Rantoul, Illinois. He was a perfect subject for an interview -- forthcoming but hardly full of himself; comfortable with the situation; ready to tell a good story. He invited me, my wife and our infant son to visit him at Piety Hill in Michigan, although we didn't follow through on that. I don't care for his Manfred Arcane stories, but most of his ghost stories seem to me at least good entertainment. A good one to start with might be "Behind the Stumps." He's a different writer from Lovecraft, but they both know a lot about creepy rural settings!
I don't see de la Mare mentioned very often. Have you read "Crewe" yet?
Aickman is, for me, an uneven writer. Don't care for "The Swords," "Mark Ingestre," etc. but admire "The Houses of the Russians," "Into the Wood," etc. Has
anyone at Chrons read his short novel
The Model? I didn't finish it, though at one time I had read a great deal of his work.
I couldn't tell you how many times I have tried to reread
Gormenghast and failed to stick with it. I think the next time, I will just have to skip some of the Prunesquallor stuff, which Peake apparently found a lot funnier than I do.
I hope lots more people will step forward with their backlog yarns. Any notable accounts of books that
had been backlog for a long time, and were read at last? One such story from me would be about Dostoevsky's
The House of the Dead, bought 27 Feb. 1975 and read at last (22 Apr. 2008-5 Apr. 2010!).