Sealed AppleCare Box Already Been Used?

[jdm.accord]

I bought an iPhone 4 from a chick today that included a sealed AppleCare Protection Plan box. I checked the serial number on the phone and it already has AppleCare on it. Is there a way Apple/AT&T put this sealed AppleCare warranty on the phone already without it being opened? My friend said AT&T does it for you at the store without even opening the AC box but I wanted to see if anyone can confirm this. Please LMK, thanks!

[Cer0]

Don't they just scan some thing on the box to activate it for that specific device. Meaning a barcode is scanned to add applecare to the device in the system.