I don't understand. The info comes from the amount of people who got the platinum trophy.
Can you account share trophies?
I probably misread this, if so, apologies.
Account sharing he meant the same digital copy being shared between two accounts that is what the actual PS Store allow... you buy in one account and share between two accounts.
So the same copy sold can be shared by 2 accounts that got the Platinum... it is probably a tiny % of users that does that but it is not incomum between trophy hunters.
That said used market and physical lending (like that famous E3 video) can have more than one account having the Platinum with one single retail copy of the game but that is even lower amount than shared accounts.
At the end it is not worth to use these in the math because it is probably not even 5% of total accounts/players.
That is the reason 9 millions players didn't means 9 million copies sold but a bit less than that like GTS that crossed 6 million players but the sales are probably around 5.5 million copies.
I think what they mean about sharing is about the actual physical copies. If I have the physical disk and platinum the game, I can then give my disk to my friend who'll play and then platinum the game as well. Two platinum's that are technically attributable to one sold copy of the game.
Account sharing is digital but yeap it is the same way than physical sharing but limited to 2 accounts only... it is more common than physical sharing but a small number no matter what.
It is a bit more common between trophy hunter friends... so each new release is one of the them to buy the game with both Platinum it.
Ohhhh one advantage of account sharing is that you can play the same copy of the game simultaneous even in multiplayer... physical you can only play one at time.