While I agree with what you're saying for the most part, I also personally subscribe to the notion that public sales (or at least sales that were publicized) trump all. My understanding is that the second sale of the AF 15 9.6 was neither public nor publicized so I give it about as much weight as it deserves as such as a strictly "private" transaction.
Also, by the time the public sale of the first AF 15 9.6 did occur, CGC had been around for what, 10 or 11 years ? By then people were well acquainted with the perils of over paying for a book based solely on it being the "one highest graded" copy.
Truth is, whether there is just one or four copies , a 9.6 copy of AF 15 is still a top of the census copy, that basically never comes available, and will probably always be one of the single most desired books in all of the hobby.
Do I think the next 9.6 copy to come up for sale publicly will fetch $2M though?
Nah.
But certainly something in the $1.3-$1.5MM range for sure.
-J.