So prove it WAS used elsewhere. I showed you where it was used , now it's your turn. WCZ , WES , WFD , no problem , they were "generic". C5ZX , C6ZX , C7ZX ,C8ZX, C5ZA, C5GA, C8AA, and MANY more were specific and not used elsewhere. NONE of these are found in ANY MPC. These were typically assembled at the Sterling axle plant SP which you assumed was "special" however generic axle assemblies was also built there as can be seen on "W" series axle assemblies that have the SP on the tag. If you need visual proof of that I have MANY generic tags that ARE in the MPC with the SP on them. I asked the question 52 years ago at the Ford Motor Company differential training class I was attending when we were on the subject of ''warranty tags". That is what the instructor told me. I still have the notes in my '68 training books.
Randy