Serial Number not recognised and different to case

I had a warranty replacement iPad at my local store. I just checked to make sure the AppleCare was carried forward from the original iPad and the serial number (General-About) is not recognised on Apple's site. The serial number on the back case is. The serial numbers differ by one digit. For example, the General-About is say 123456789 and the backcase is 113456789.

Has anyone had this happen to them before? I want it corrected as I will probably sell it at some point and don't like this discrepancy plus the 'not recognised' status online. But it's really irritating as I have just fitted a Otterbox screen protector and case. The case I can't get off (a problem a lot of iPad 1 owners have reported a similar issue).