For the longest time we had no info on phenolic handled knives from 1972 to 1986 because they all were stamped the same, BUCK, 119, U.S.A. Then the issue of the micarta spacers was brought up. I took several hundred of each of the 100 series modles and laid them out on the floor. Some of the knives had boxes with dated paperwork which helped out a great deal. After studying the mess I had made I came up with the following, which I will concure, is based on several assumptions.
1973-1980 blade stamped BUCK, 119, U.S.A. Guard has 2 micarta spacers and pommel has 2 micarta spacers.
1981 blade stamped the same. Guard has 1 micarta spacer and pommel has 2 micarta spacers.
1981-1985 blade stamped the same. Guard has 1 micarta spacer and pommel has 1 micarta spacer.
I have only actually seen 119, 120, a couple 121's and one 118 with the spacer combo explained in the second group above. Lots of 119's and 120's. It is possible that most models skipped this variation and went straight to the third group.
I have no clue on the snaps but I know that a few years back we made a batch of flap over sheaths, just before all the sheath making machines were gone, and they had the snap you described with 3 bucks in a circle.
I hope this helps.