In 1995 in the spirit of open government, President Clinton signed a declassification order which rapidly brought many formerly secret files kept by the government to light. However, our CIA and other agencies did not accept that many of these documents should be public knowledge, and immediately began “reclassifying” documents. They began a secret review which then accelerated under the Bush Whitehouse. Thirty or so reviewers, mostly CIA and defense related agencies work in a million dollar safe room deciding what is fit for public consumption. Important things like the CIA's failure to predict Chinas entry into Korea two weeks before it did. Historians who have ferreted out this reclassification say that many of the reclassified documents are just ridiculous. Many they say have subject matter that has no relevance to national security, or was published in government studies that are public knowledge. The reason for this I would speculate would be to create white noise. Like writing over computer data with rubbish, to make the real targets disappear in the ditrious. At any rate, this wholesale rewriting of our countries document history is Orwellian.
Read more in this link to the NYT and the story written by Scott Shane.