Screenshot showing Jimmy Carter's request
In 2002, former President Jimmy Carter asked the State Department to release previously declassified documents on U.S.-Cuban relations, according to a listing of declassification reviews.
Carter made at least 39 additional requests for the declassification of State Department documents in the 1990s. His requests were granted, which I imagine then allowed Carter to make public and write about the documents without violating any secrecy laws.
The State Department listing doesn't give details about the documents.
I came across Carter's requests in a massive 1,400-page PDF, which was posted on the GovernmentAttic website in October. I am preparing Freedom of Information Act, or FOIA, requests in connection with my research into U.S. government programs in Cuba. (See Cuba Money Project for details about that). Scanning FOIA logs and reading letters of others who have made FOIA requests gives me some insight into how these things work.
The State Department PDF shows a log of declassification reviews performed from 1974 to 2010. You can download the 77.5 MB document from this GovernmentAttic page.