Thank you for sharing. If you have the cover itself (stamp or postmark/cancel), then please share that image.
I don't know about KOC but here is some additional information.
As you probably know, CAPO is an abbreviation for Canadian Army Post Office. There were 8 types of Canadian War cancels used around Newfoundland from about Sept 1, 1941 until July of 1946.
These were primarily in Newfoundland, Lab or adjacent areas of Canada. Remember Newfoundland was a separate country then and had their own postage. There may have been CAPOs in other parts of Canada. In Newfoundland, according to the NSSC:
CAPO 1 - St Johns
CAPO 2 - Gander
CAPO 3 -Botwood
CAPO 4 - RCAF Gander
CAPO 5 - Torbay
CAPO 10 - Goose Bay. The one you shared is from here. Postmarks exist from Goose Bay from July 2, 1942 to April 1, 1946. If you have the cancel date and its outside these dates, then it would be valuable and likely rare. Unlikely though.
There were also related Armed Forces cancels (Not CAPOs but similar):
Avalon F.M.O.
Avalon F.M.O. #2
I'm lucky to have an exemplar of each. Here is one to share. Note that the postal cancel has CAPO #1 in it.
