How can I tell if a book title would be included in Kindle UNlimited?
You'll see this:
The funniest thing about this particular signature is that by the time you realise it doesn't say anything it's to late to stop reading it.
Right there on the book's listing page.
If all else fails, Amazon is 24/7 at https://www.amazon.com/contact-us
NOTE: I do NOT speak for or represent Amazon in any fashion. This is a customer to customer forum.