Nissan Rebate Question

[Salsy1]

I am buying a Nissan truck for winter, and it has been assembled and is en route to the dealer where I ordered it. Nissan just ended a rebate of an additional $500 for the Columbus day holiday. The rebate ended this past Monday.

My question--- How do I know that the dealership isn't screwing me out of the $500 rebate by telling me they haven't received the truck yet when they possibly could have? Is it possible for them to fill out the paperwork after the truck arrives on the last day of the rebate, then call me a couple of days later saying the truck is in and finish the deal (and me getting the shaft on the rebate)? What does Nissan look at to determine that the truck was sold during the rebate period before they shell out the rebate money? Is it the primary bill of sale? What prevents the dealership from claiming the truck was sold a day or two earlier and keeping the rebate for themselves if the vehicle was delivered to the dealership during the rebate period?

I live too far away from the dealership to drive down there and check out their parking lots. Thanks in advance.