Caledonian continued to use the KT
code for some time after being re-branded from British Airtours, I flew MAN
in October 1990 on G-BPEB, they were still using the KT
code then. The CKT code was introduced a couple of years later.
As I remember, the KG
code obtained and used for Caledonian's no-frills charter services, initially under the Atlanta Airways/International Airways banner, to distance the cheaper service from the Caledonian brand.
These flights were mainly flown by appropriately registered G-CEAP!
I think they continued to use the KG
code when the no-fills operation was re-braned (again!) as Peach Air, when flights were operated by 2 different airlines under the same brand - Air Atlanta (TriStar) and Sabre (737)
Hard to believe it was that recent - seems like much longer ago!