cpp spindle question?

[kevmar96]

So I ordered a set of spindles from summit. When they arrived the box said part # cp4s3 which is supposed to be 71-72 2/12" drop spindles. When I took the spindles out the casting on the spindle said cp4s4 which is for the 73 and up c10. I called summit and they said to send them back, which I did. They replacement spindles arrived today. They Have The same casting of cp4s4. I called summit again and they called cpp and put me on a 3 way with cpp and the guy there said they use the same casting number(cp4s4) for all their spindles then machine them for the different years. He assured me that these were the correct ones but I can't understand why they have the same numbers on spindles for different years and no other numbers to differentiate them from one another. Why make it so confusing. Maybe it's just me. Was wondering if anyone else has used these spindles on a 71-72 with this casting #. Sorry for such a long post for a simple question. Thanks For Any help.