Looking at various build dates, here is what I have seemed to find. The earlier (looking only at Dearborn on these particular cars) 1964-early 65 cars seem to have originally had gold door latches. The later ones appear to have a clear zinc or maybe cad. plating (in other words, it's silver) and the latch "teeth" and rivets that are marked "L" and "R" are gold though.
I think that is what I am seeing, but it is difficult to determine because the gold plating on those early ones is really thin and does not hold up at all. Most of it is kind of worn off with the silver/clear under it.
Any other observations?