During WWII the Allies in the upper command echelons had a good knowledge of what was happening in the KZs from several sources the most notable being the Enigma Decrypts, others included testimony from escaped KZ prisoners and POWs as well as 'ransomed' jews. As late as 1945 many of the Allied troops at formation level had no idea of the horrors being perpetrated in the camps - one of the reasons given for this was the protection of the Enigma Secret. Also I think the case existed for compartmentalising intelligence - an intelligence unit may have knowledge but it would not be passed on for general consumption. There were many groupings of prisoners in the KZs including SOE/OSS agents, Bomber Aircrew (classed as terrorfliegers), commandos etc. In some cases their fates was not known for several years post war.