That Hinsley quote is from the official multi-volume history of British intelligence during WWII. Additionally, I would point out that it is common in survivor accounts to say that "selections" for gassing were regularly performed on
registered prisoners. So then the registered/unregistered distinction which they cling to with utter desperation doesn't even work. The registered deaths in the decrypts also confirm the 1942 typhus epidemic along with the very high rate of registered deaths during that time (which dovetails with revisionist interpretations of Auschwitz). Mattogno's recent book The Making of the Auschwitz Myth goes into this topic.
There really isn't much to respond to here since (for the most part) they aren't truly disputing the revisionist position. Revisionists say there is no evidence in the decrypts for Auschwitz being a mass murder factory, nor for the "final solution." HC is implicitly conceding that this is correct. Notice HC doesn't say the decrypts prove the holocaust. Rather, they are reduced to arguing that the
lack of evidence is "expected"! If the holocaust were true, we should see its reverberations all over the place. They are only saying otherwise because they came up empty on this so have to contrive excuses.
The implication of their argument is that the Jewish extermination was a very closely guarded secret, so secret it could not be mentioned even in encrypted communications where matters of
vital military importance were discussed. The ONLY evidence provided for this is a document where it says not to send messages of the highest security classification. Even if that's true, it assumes 1) that everything holocaust related would have been classified that way, and 2) that they respected the classification very strictly and never slipped up. Except sometimes in public speeches.
The Wikipedia page on ULTRA quotes historian Andrew Roberts as follows:
Because he had the invaluable advantage of being able to read Field Marshal Erwin Rommel's Enigma communications, General Bernard Montgomery knew how short the Germans were of men, ammunition, food and above all fuel. When he put Rommel's picture up in his caravan he wanted to be seen to be almost reading his opponent's mind. In fact he was reading his mail.
Clearly, the Germans did not know or believe that the British were reading their communications. David Irving in his Churchill research found that Churchill in some cases was aware of when and where the bombing raids were set to occur because of decrypted messages (he mentions Coventry specifically). We are to believe then that the Germans revealed important military secrets over radio but they were so committed to secrecy on the Jewish extermination that they kept that even more secret. Rubbish. This hyper-secret holocaust theory is also inconsistent with the fact that already in 1942 there were claims of Jewish extermination appearing in the newspapers.
