Of course, there are books that genuinely do appear rare and enough time has passed to make that call. A good example being the 1st impression of the 1966 Unwin Paperbacks Hobbit. I only know of 12 copies (I have one of them, found by pure luck).
If Luck you call it 😉
The 1st Unwin PB Hobbit is a great example of an actual scarce (my term) item. With only tiny amount known to exist. Another great example that comes to mind is the Unwin Hyman 1987 Unfinished Tales, with as far as I’ve seen only a handful of copies known. Items like these would fall into this category IMO.
Yeah, I agree. I think of all the books I own those would probably be the only two I'd really consider "rare" in my collection. I guess also the Child's World Oliphaunt, simply because that was withdrawn from sale very quickly after release, so there was only ever a tiny window to buy it (and I haven't really noted any coming up for sale since -- though I know Emilien found one last year). Most Tolkien stuff seems to be available fairly easily if you are willing to throw enough money at the problem.