Western's fillet knives actually had S-W model number descriptors. The "S" is for stainless steel (440A) and the "W" is for the wood handles.
The S-W76 came out in 1968, with an OAL of 11" and a blade length of 6". These obviously do NOT have date codes.
Then in the 1978 catalog, the Western fillet knife options expanded to the --
S-W764 FISH/BAIT Camp Knife with a 4-1/2" blade, with an OAL 9"
S-W766 Fish Fillet Knife with a 6" blade and an OAL of 11"
S-W769 Super Fillet Knife with a 9" blade and an OAL of 14"
All three had stainless steel blades and wood handles and should have date codes.
The S-W764 was listed in the catalog pages as the "Fish-Camp Knife", but both specimens I own are ricasso stamped "BAIT CAMP"
After Coleman bought Western in 1985, they came out with a rubber handled line of fillet knives, again with stainless steel blades (440A) in 1986. All these should have date code stamps.
966 - 6" blades, 11" OAL
967 - 7" blades, 12" OAL
969 - 9" blades, 14" OAL
9612 - 12" blades, 17" OAL.
They continued the W766 and W769 models, dropping the "S" from the model numbers but retained the 440A blades.