The nature of released files, as well as the released FBI files
This does assume that there is a monolithic government agency with all those files, perhaps even reflecting a monolithic government opinion about what's going on. But as any one knows, the federal government and all it's various branches are perhaps as fragmented as the ufological community, and perhaps with as widely divergent a number of opinions as to what is going on.
Also the opinion of what is going on with UFOs, as refected in various Estimates of the Situation, is undergoing ongoing evolution as well. This much can be discerned from what documents are currently available, especially evident in the late '40s and '50s.
This also presupposes that all relevant documents are available. Ruppelt, in the late '50s, tells of his attempt to go back over the Mantell files and discovery that portions of the microfilm were no longer readable even then. Anyone who has ever had the misfortune to try to use microfilm realizes it's downside as an archival material, even though it was the wave of the future for way too many years.
For a view of just how difficult it can be to deal with microfilmed materials, as well to get an idea of the variety of opinions and volume of documents out there, try looking at the UFO files released by the FBI to ameliorate the ever growing number of FOIA requests they were inundated with. They can be found on an official FBI website,
here.
And who knows how many files are out there that were generated simply for the purpose of disinformation, a la Bennewitz and the MJ12/Aquarius files, to say nothing of files that can perhaps legitimately be classified due to national security matters, whatever that means.
Cthonic Charlie, the Cataloging Curmudgeon