I originally envisioned the focus of the thread to be desirable books from 1935 until the end of the war (generally), to see (initially, then over time) which books maintained extremely low counts.
Books that you would think would have many copies slabbed, if they were out there.
There are always going to be people like me who have never slabbed anything, so actual numbers will never be ascertainable, but I love it as a book to book comparison tool.
It is going to be fascinating over the years to see which books had 6 copies in 2017, and now have 7, and may still be under 10 a decade from now.