200 Year Old Report Declassified

Everyone knows about government secrecy so it should come as no surprise that reports on such topics as cryptography are classified. Sometimes they remain that way for centuries. A recent article reported that the NSA is declassifying a report on the subject from 1809. The act was done to comply with Obama's memorandum about Open Government. However it begs the question, if something such as this is classified what else does the government hold behind closed doors?