According to Anandtech, Asus says that the 1403 BIOS adds support for Kentsfield. I am guessing that the entire 14xx series was meant to add support for it but they did not realize that the 1401 BIOS had leaked, so they said 1403. It might be that they finally figured out how to get the BIOS to support Kentsfield and function properly in 1407.