Yes mass conspiracies w/ coverups are very possible. Holocaust after all was one, with a documented cover up, and you can see how well that turned out, with them leaving behind thousands of incriminating documents and enormous quantities of ash at supposed killing centersI'm not going into 25 back and forth with you again, and you already know why.
You said coverups were impossible. That's wrong. Coverups are possible. I appreciate that you can acknowledge that, now.
I think a better question is whether a given conspiracy is likely. Some, like David Irving, speculate the Holocaust did happen, but it was the Jews that inflicted this wound upon their own body by intentionally provoking the Nazis so as to gather future sympathies. Some say Hitler was Jewish or possibly an agent of the Jews. I talked to one holocaust denier who said he thought the Jews really have done nothing bad in the world, but are being scapegoated by a still more elusive group.
So is it likely (forgetting for a moment how many people involved ended up outside of the iron curtain) an entity like the USSR covered up the existence of each and every resettlement camp, destroying or concealing millions of documents, suppressing millions of witnesses (who didn't talk even after the USSR fell) when they couldn't cover up an operation probably 1000 or 10,000 times smaller? (Katyn)--on top of all the Holocaust "proofs" they also manufactured
Call me crazy, but I say no, and to be honest, I don't even see a motive on their part. EG the soviets were basically holocaust deniers, in that usuallythey didn't put the Jews front and center, or even mention them
the famous Auschwitz plaque:
the new Auschwitz plaque, created after the fall of the USSR:
Soviet textbooks didn't mention Jews:
So why believe in such a conspiracy? I'd say it is mostly the domain of anti-semites and 'white advocates' who are afraid of giving the Jews the ultimate victim card, but I'm open to other theories here