From the National Security Archive: The CIA does not want to release the secret final volume of its internal history of the Bay of Pigs because people would get "confused." The problem is that the CIA disagrees with its own historian:
A 400-plus page report by the CIA’s inspector general critiqued the invasion. Pfeiffer, the CIA historian, in turn critiqued the inspector general’s report in the still-secret fifth volume of his history. Pfeiffer’s supervisor, though, called the volume a “polemic” troubled by “serious deficiencies,” and said that it would not be published.
“Dr. Pfeiffer’s account (was) an uncritical defense of the CIA officers who planned and executed the Bay of Pigs operation,” the supervisor, J. Kenneth McDonald, later stated.
This is the Bay of Pigs we're talking about. It's already a well known foreign policy disaster and has been for, you know, over a half century. It can't get worse!
I see the CIA's point, though. It's confusing to hear a government agency deviate from a single programmed line. We're used to lockstep and our brains might explode if we're suddenly faced with something else that requires thought.
I like the point that the Constitutional Convention records were only sealed for 30 years and we know how contentious they were and how much higher the stakes. Rip the band-aid off, release the book, and move on.