The revelations about the VENONA efforts changed dramatically how scholars talked about the role of Soviet espionage during the war. For example, the Rosenberg case went from a "did they do it?" question to a question of "how much did Ethel do and was the death penalty an appropriate punishment?" question. It changed assessments of McCarthyism (there were some spies in those accused, but also many not) as well. So that was pretty substantial from a historiographic point of view.