Originally Posted by T-Mar

Agreed, the 1st two characters are reverse format of what I would expect on a Bridgestone manufactured product. Unfortunately, I don't have any S/N data for other aluminum frames, so I can't offer an explanation for this. However, to the best of my knowledge, Bridgestone never incorporated size codes into the serial number. Certainly none of the Bridgestone S/N I've collected indicate this, though there is the odd case where coincidence could make the 3rd and 4th characters appear to be a size code.