I take that back because 1. I have Verizon so the serial numbers are different & 2. I have a "certified pre-owned" iPhone 4. I just checked & my AppleCare end date is wrong. I purchased my iPhone on 11/29/11 & my end date is 10/6/11. My guess is it was returned within 14 days & not refurbished.
Apple does not replace units with refurbished models. What you will get as a replacement is in fact a "Re-Manufactured" unit. There is a big difference between the two.
However, people seem to believe what they'll get is a refurb and this incorrect assumption prevails amongst the iPhone fateful.