Having been involved with the declassification review of the Army’s WW2 records during the mid-1990’s after President Clinton’s declassification order, everything that was declassifed by General Eisenhower’s declassification order in 1947 was reviewed and declared unclassified.
The problem isn’t the declassification of records or records being “hidden or withheld” it is just that there are so many of them, that folks have not reviewed them at the National Archives building in College Park, MD. And having done research in that archive, the finding aids are not that detailed.
We are talking about tens of thousands of linear feet of paper records to go through. All one has to do is go to the National Archives, get a researcher’s card, go to the reading room and using the indexes they have, request the file boxes you want to review. See https://www.archives.gov/research
Tell me that many pertinent records did not wind up in Sandy Berger’s socks. Patton was outspoken about the Soviet threat, the infiltration of the U.S. government by Soviet agents and the U.S. role in the slave trade agreed to in the Yalta Agreement. Most comments concentrate on his possible murder in the hospital but the traffic accident was suspicious. It may have been an accident, however knowing how dirty the government was it would not be beyond the realm of possibility.
For example, Bruce Lee's path-breaking Marching Orders recounts numerous discoveries he made in the records of of the intelligence analysis of high-level Japanese and German codes during WW II. Yet he was denied access to some records and was told that they would never be made available to researchers.