Chomsky had an explanation for why most of the world unquestioningly believes the USSR was the true socialist/communist expression - propagandists from both the worlds superpowers wanted it that way for the better part of century. Socialism/communism appealed to post-recession Americans, so the political right pointed to the USSR dictatorship as the inevitable result, and on the other side Stalin and his successors were rolling in socialist rhetoric (being a philosophy widely regarded at the time to be morally superior) to cover the stink of dictatorship.
In the end terms mean what people want them to mean, and that changes over time. My brief reading of Engels
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