Thanks. I never bothered to verify years. I just fixed or changed ratios on whatever came into the shop. It is totally possible the rears were replaced in the early cars with later units.
But that does seem strange to me. As that would mean there were only 2 years (73 and 74) of SBP 7 1/4 rears, and I have seen many more SBP threaded rears then LPB