Does anyone know how to decode the letters that are sometimes at the ends of Jeep part numbers? I've checked my parts catalogues but it was of no avail. For example, I was looking at water pump numbers. The number for a '97-'98, 4.0 is 4626 215. For a '99 it is the same number but adds AD at the end, and it does actually seem to be considered a different part. Other parts sometimes have an AA or AB at the ends. This isn't really a big deal; I just am curious, as I like to learn how/why things are as they are.