The guys on Bladeforums (Buck Knives sub forum) said it has to do with "macassar ebony "wood
Macassar ebony is highly variable. Some pieces will have nice black/brown stripes, some pieces will be mostly almost black, and some pieces will be mostly blonde. If this has not been messed with since it left the factory, you probably got two mismatched macassar scales.
The thread kinda drifts to arguing about dating, and 3 pins , 2 dot, what year the added this dot, or whatever!!
But, it's still an informative read
I'll just call it "late 70's"....;)