Weetabix could be right about that, here are pics of the left side of my '76 and '68, it looks like to me they both were originally stamped, 9mm ,,P-64" and the Cal. Makarov and x18 was added later either by the exporter or importer to satisfy BATF. And then to really start a squabble a bunch of the sellers were advertising and calling them the Polish P-64 Makarov, which we all know that the P-64 is not a Markarov pistol but a P-64 Polish 9x18mm, [acronym - -CZAK].
Wow thats wierd I never noticed that, my 1969 is stamped the same way. After I saw your pics I looked closer at mine. Thanks guys, learn a little more everyday.
I too have a 1968 model with the round hammer, and I found that the hammer tension and trigger appear to be heavier (at least to me) than the 1974 model a friend of mine purchased at the gun show last week.