I can purchase a wand, and Modify Charges (say, to 12)
I can purchase 2 wands, and they show as "Wand of Aid" with a quantity of 2
If I a) modify charges after purchase
or b) buy 1, modify charges, buy a 2nd
then I end up with 2 wands with the same reduced number of charges.
This is true both in the Inventory Screens and in the output displays.
pathfinder core set