The Ford Motor Company documentation system was based on "simplicity". Most companies today have a "engineering drawing" (or a "specification document"), one that details the requirements (dimensions, materials, finish) for a supplied part and a second document that provided "approved" sources, maintained in the purchasing department. Ford had combined the two documents, the "measurement" and "source", into one from it's first days of production. It was one less piece of paper. Note: Ford was source - singular; the two document system was sources - more than one source. As a result, for any new source for that "identical" part, Ford had to create a new document, and a new part number. This is probably what you are seeing here with the multiple Ford service stock numbers, which were derived from the original engineering numbers. It's the 'Ford system".
Jim