SOM Old Stupid System: Used floppy disks
SOM New Not Quite as Stupid System: Uses authorization codes on little pieces of cardstock. You type in these long alpha-numeric codes in order to access the season's you've bought (e.g. the HOF "disk"...which is really no longer a disk).
So when you're order comes you get one CD, a little piece of card stock with each set you bought, as well as another piece of card stock for the latest year that you get automatically with the order.
hope this helps.
P.S.: Don't lose those little pieces of cardstock...