150 is highly likely still too low. 200-250 is highly probable imo. And my opinion is based on a myriad of factors
1) certified copies ( not just cgc but cbcs and , gulp, even pgx)
2) known raw copies (that's the number the avg person likely has no clue, and the reasons I believe many estimates low )
3) some "common" sense to me. I've owned 15+ copies of each book. My experience tells me it is highly unlikely that iVe owned 10% of all existing copies
4) extrapolating from fellow collectors /dealers that know of copies I don't, etc
Your modesty is understandable, maybe even spot on. But, this is far from a random sampling effect. As a dealer who specializes in such books, it makes the idea that you or Metro and a few others may have indeed touched 15% or more of these two books as they came up for sale logical, even probable.
Then again, the math would be trickier than simply counting copies owned or sold by any one of you since your 15 copies had in all likelihood been also sold by some of the others too at one time.
that's the key...I might have touched 15% of all copies sold over a period of time, but I know I haven't touched 15% of all copies that exist (imo)... so one does have to differentiate...
I'm thinking metro has likely sold 50 copies of each alone, since they started dealing...many raw, restored, not slabbed and not "known"... and that just them...think of all the dealers from the 70s-90s that sold raw copies that are still out there raw...trust me, it is hundreds!