I would suspect that Canada, Australia, and South Africa (at least) may have had their own official S&W .38 revolver nomenclatures, aside from that used by England. It seems probable the ".38/200" or "K-200" were never official designations for the S&W BSR used by any of the British Commonwealth militaries. I'd say "Pistol, Revolver, Smith & Wesson, No. 2 (or .38-in)" would be close to being "official."