“meaning the other 59 million must still be using the PlayStation 4.”

That’s not what that means.

As of last December there were still 2 million active PS3 users.

playstationlifestyle.net/…/ps3-monthly-active-use…

I’d imagine there’s still a limited number of PS Vita and PSTV accounts too.

I stopped at the PS2…

I don’t think PSN applied to the PS2, started with the PS3.

PS2 didn’t have networking apart from the odd firewire port and a very expensive devkit.