Searching the net, I found this advertisement for a knife that was sold. This is not a coolie capped knife... but it is 1961 and importantly, it apparently has a recessed tang nut (unfortunately no picture of the butt).
If I have interpreted his term "recessed tang fitting" correctly as referring to a recessed tang nut, this moves the start of the sometimes use of reversed-hidden-recessed tangs back to early '60s which could impact how we view the progression of coolie capped knives and their tang nuts. The dealer is well known, I've bought from him and trust his judgment. I've abbreviated his text.
Special Order Randall Bowie Knife
Custom Made - Model #12 Grind
8" Tool Steel Blade
Forward Curving Double Brass Guard
Scalloped Brass Collar
Beautifully Aged Ivory Handle - Commando
Escutcheon Plate w/Original Owner's Name
Scalloped Brass Butt Cap w/Very Rare Recessed Tang Fitting
Rare Jim Stockman Sheath w/ Brown Buttons
Two Tone Combination Crystolon Sharpening Stone
(Made in U.S. of A. w/Blue Print)
"My summary: a vintage 1961 special order Randall Bowie with ivory commando handle and brown button Jim Stockman sheath for consideration. This knife comes with a letter of provenance from the original owner detailing approximate date of order and delivery. The owner requested a scaled down (presumably model 12) blade of 8" and the Randall shop obliged. (they still allowed custom orders back in the early 60's) The handle was taken from specs in the catalog -- the Jim Stockman sheath then made for the knife.
"The letter from the original owner as follows:
'Concerning Randal Knife that I sold in April, 2007. I special order this item from Randal Knives in Orlando, Florida, around April or May of 1961. I was stationed at Marine Barracks, Jacksonville Naval Station. The handle was taken from Randal's catalog and I scaled the blade & mailed order to Orlando. Upon receipt I mailed the knife home. I was discharged Sept, 1961, so received before that date. The knife, sheath and stone are exactly as I received them from Randal. The ivory handle cracked many yrs. later. The above description and time frame is as accurate as I can recall.
Sincerely,
H.D. Tindall'"
"The brass hilt is forward curving with a scalloped brass collar between it and the commando handle. The handle is ivory and has aged quite nicely. The brass butt cap is scalloped and over an inch long. Most notable is the recessed tang fitting -- this is the first Randall knife of any kind that I've seen finished in such a manner. The rare, custom brown button sheath was made by Jim Stockman."