Okay, I should not have used the word 'rarely' but certainly much less than today. In 2008 it looks like about 180,000 books were slabbed with maybe 1/4 from the current decade. In 2016, 400,000 books were slabbed with about 150,000 from the current decade. In 2008 ,Moderns were not nearly as speculative as today.
Bob, there is an ever increasing number of all slabbed books.
I think it took 8 or so years for CGC to reach their 1st million books and about half that time for them to reach their 2nd million books. I think we're easily at 3MIL now if I"m not mistaken.