If I recall, and it has been awhile, probably around 2008 or so, my newly purchased 2000/3000 upgrade drivers for older cabinets used Dayton Reference drivers(or were spitting images of them) that were aluminum coated, not all aluminum like typical aluminum drivers can be. It wasn't all shiny, but more of a gray colored cone with a nice aluminum phase plug.
I imagine John and company use what is available at the time for their upgrades. FWIW...