I think maybe a larger, more overlooked number of these books are probably in big boxes in mom and dad's attic that Johnnny left at home when he went away to college, the Army, whatever , and forgot about. Seriously, I would guess there are thousands of copies out there where this has happened. There are a lot of people out there(mom and dad) that think the only worth those comics have is nostalgia and memories, and wouldn't even think about trying to sell them. Plus a lot of those people also probably have never even seen eBay to try and unload them. And if that is the case, they definitely won't know what cgc is...
Not saying thats the largest segment of where those 202,000 copies are, but I would bet it's probably a decent sized number.