Ok, so I have to ask when you received these 9.9+ grades. I’ve only had around 500 books graded and my opinions are shaped by my experiences and the experiences of others I know. Based on that I’m of the opinion that the vast majority of 9.9 and 10 grades were given out many many years ago.
Honest to God I just picked a title out of thin air that I know has been submitted heavily to look at the numbers at CGCdata.com. Wolverine #1 from 1982. The book has had ~ 22,000 subs since CGC was founded. It has 27 9.9s and 3 10s. However of the 22,000 subs ~8,000 of them have come between Jan 2018 and now. Of those 8,000 copies there have been zero 9.9s and zero 10s.
now obviously this is just a book picked randomly but I’d be willing to bet that this isn’t an outlier.