Guess we'll never know "why" all again subjective, but my guess was aside from the "cost" ( buy from the low bidder) they wanted it to be different for the 'new models' coming out in 1973, so folks could "see" in a glance, one is totally different ,,,newer?? , than the other, renowned 'black eagle' old models....as for pins versus screws ,most folks today still do NOT "see, know, understand", there is a difference till you tell them 'transfer bar'.....
put a pair of grips with black eagle medallions, on a 'new model', and they 'think' its an 'old model'.....human nature, makes them STOP, LOOK, and pick it up to discern what they actaully may have in their hands.........
anyway back to 'beggers' question, the change was in the early,mid 1970s, and yes across the model lines that used the larger medallions, Bearcats Security Sixes, etc., used te smaller sized, all silver medallions.........
again,all spelled out in the many books that have been written over the years, in 'detail'....one may not be able to "remember" it all...........
wish I had a digital camera, or even cared what came on what gun back then, let alone take a picture of it :roll: