Rocky, your Sun Valley knife is a rarity to me. I looked it up in Gaddis. The design was proposed in 1957 but apparently the first knife wasn?t made until the end of 1960. And apparently there were only a few made until the design morphed into the bear Bowie in 1963. Of course that is actually a "flanged butt cap," not a "coolie cap." As we have noted, the first such cap reportedly (by Gaddis) adorned the famous King Faisal set shipped in early 1956.
However, that presumably recessed tang nut on that Sun Valley was some truly new information. It has me looking at every early ?60s knife with a brass pommel hoping to find more. Significantly, now two RMKs in the 1959-1961 span with a recessed-hidden-inverted tang nut using the slotted "nut," yours and (possibly) the one sold by SteveZ. That makes your knife one of two to date, which qualifies it as being ... er ... pretty unusual.
The use of this system in late '50s is a seemingly new fact to my knowledge only previously mentioned by Steve Z in the ad for that Bowie. And we have a new mystery ... why was this system tried and then put on the shelf for another 10-12 years (if it was)? It will be interesting to see just how extensive the use of this slotted recessed tang nut was in RMKs in the late 50s, early 60s. Amazing the tributary information that surfaces.
Another point, this one about recessed tang nuts with those slotted ends. They were not new when Mr. Randall experimented with them first in '59-'61. They were used on WWII British commando knives, on Swedish knives, etc...all showing that slotted end.
