You seem to know a lot of specific details about these weird books. Does the library force you to read them before you put them on the shelf?
Read them
through, no. Check reviews and sometimes skim over parts (to confirm review contents, among other things like condition or printing error checks), yes. You pick up a decent amount doing that, particularly if you read fast enough and/or are (morbidly) curious enough to take a moment scope out a page or three just make sure you're not hallucinating and, yes, that actually got published.
Yes, it actually got published. Iirc the pyrophilia one sent us multiple copies as a promotion for their book (we yeeted the lot; beyond the magical forest stuff the writing was remarkably shit and the general subject something our patrons don't circulate much).
Why would helicopter blade aerodynamics count as an odd book?
Disk loading, ground effect, wake effects, auto-rotation, all good stuff!
It's a rural public library. There's functionally or literally no one within like an hour or better's drive that would have need or interest in a helicopter blade aerodynamics technical book, and it's wildly at odds with patron interests or the rest of the collection (too specific, not to mention that particular one was a good 15+ years old). It was odd it was still in decent-ish condition, and odd someone thought it was a good idea to donate it to a general use public library at all (though think is a strong word a lot of time, from what I've seen. We appreciate it and try to treat donations better than most things, but I'm pretty sure some folks just dump old book collections on us to clean out space).
Mostly it was just that it was a hyper focused subject matter; most of the time that sort of technical writing doesn't make it into the general population to get donated to us to begin with.
Hey, recreational mathematics is fun! And not that obscure either. Conway's Game of Life first appeared in a recreational mathematics column, I think.
Some degree of it isn't that obscure, but these weren't a column or part of a general book of puzzles or whatever; it's literally a journal series of recreational mathematics.
That, specifically, is pretty unusual. Not super unusual, but like I said, probably in the top ten or so most unusual I've seen in the last year or two.