Others, like this one from a damaged book or a book that has little value for one reason or another, I determine that the bookplate would be better displayed by itself. Storage considerations creep into these decisions, too.
Appropriately, this Training School Library bookplate from State Teachers College in Kutztown, Pennsylvania became my training school in ex libris removal. As you can see from the photo above, it was successful. For that I thank Molly1216 on YouTube. The best instructions I could find were in a YouTube video. For me, actually seeing a task performed, makes it much easier to duplicate and eliminates any confusion that might develop from written instructions. Molly1216 (YouTube user ID) has an interesting series of book-related videos, one of which was removing a bookplate:
Not on the video: You may have to repeat the procedure. My bookplate was still sticking after 30 minutes, so I repeated the process and 30 minutes later, it lifted off the board perfectly. Drying out, the bookplate wants to curl up a bit, so I kept it flat between a folded piece of wax paper for about 24 hours, pressed with a heavy antique iron. Any heavy object will do. I first had the bookplate wrapped in paper towels (to absorb extra moisture), but noticed the paper towel starting to adhere to the bookplate's backside, so I switched over to wax paper about four hours into it. I did not use the watercolor paper to treat the book cover because my book cover that contained the plate was detached from the book and was discarded. But the watercolor paper might be useful for drying out the bookplate further while being pressed flat.