I didn't receive any instructions about not deregistering the PWs. They only asked to have the WiFi turned off. I have always deregistered by doing a full factory reset before returning any electronics item. Amazon has serial numbers and order numbers with which to verify any returned item.
EDIT: And the fact they emailed me that the items were successfully returned and that charges would be reversed indicates they were able to track these units and associate them with my account/order.
Currently: Kindle Touch, iPhone 5, and iPad 3.
Last edited by jswinden; 10-21-2012 at 02:40 PM.