Re: Partial truth, partial cover up ?
pretending to believe that such a highly detailed cracking was faked decades after those alleged spies needed protecting makes no sense.
Enigma machines were handed out to allies who weren't told that they were broken - so the UK/USA could read the secrets of 'friendly' countries for decades.
To keep the USSR underestimating the achievements of western cryptanalysis in the hope that they would be less careful/put less effort into advanced codes. Pointless wiht the number of KGB agents working for MI5
Possibly most important. To prevent the story that the Nazis only lost because of crypto becoming a political norm in Germany. If you lost because the other side 'cheated' then there is a justification to try again ( but this time with better OPSEC). Similar to the German belief that their army was superior in WWI but had been betrayed by traitors at home - so if they could only remove 'non-Germans' they would be victorious and so it was worth trying again....