Letters at ends of part numbers

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.

i think they are revisions in the part, such as when they change casting to fix a known problem.

That's kind of what I've been leaning toward. Thanks. Anyone else have an idea?

I work at a jeep dealership parts department,we have always been told that it is a revision or upgrade of the previous part or the supplier has changed, we have had instances where we could not use a "AA" part and HAD to use a "AB" part for warranty replacement.

vette75406 said:

I work at a jeep dealership parts department,we have always been told that it is a revision or upgrade of the previous part or the supplier has changed, we have had instances where we could not use a "AA" part and HAD to use a "AB" part for warranty replacement.

Click to expand...

Okay, then as to the example in my original post, would a water pump without AD on the end be able to be used in place of my '99 which lists the AD? I'm having a very hard time finding any that either directly match, or even cross reference specifically to, the AD part.