I have no knowledge of how Mopar does p/n's (but that doesn't stop me from giving my opinion!
) but I think the letters, particularly the last letter is the revision. Different revisions are typically functionally equivalent but have differences that may or may not be visible or detectable. For example, the exact designation of the substrate may have been updated to a more modern, available, less expensive, more durable, and/or more moldable compound. The only real way to know for sure is to compare the engineering drawings.