The Blend Date listed on your window sticker (available for download here) isn't the car's "official" build date but, rather, the date the chassis and body come together on the Flat Rock line. As explained by Iceman5000, the build usually starts a day before and finishes the day after. For example, my car's Blend Date was 20121017 (17 Oct 2012), but its "official" production/assembly date (listed on the GT500 Certificates of Authenticity I purchased from Ford) was 16 Oct 2012.