As I recall back in the 90s when the Dems (either Kennedy or that old marxist from Ohio -- can't recall his name now) released Clarence Thomas' FBI file to Nina Totenburg of National Public Radio. The distinction is the so-called "raw file" and any files created as a result of a formal FBI investigation.
A raw file is background information gathered via interviews with people who have known or worked with an individual. It could be anyone from your boss, co-workers, neighbors, old lovers, a high school teacher to the guy you beat up in 3rd grade. None of the information contained in a raw file is varified or placed in context unless the FBI feels that some charge or information gained requires further investigation. The raw file is really nothing but hear-say and is never released. Any follow up investigation (if there is one) becomes an official file that the target does have a right to see.
At least that is my memory of the explanation when Clarence Thomas' raw file was flashed all over the news because dirty Rat tricks.
So Reid might have been looking at a raw file? That's even MORE horrifying to me. Maybe the FBI needs to look at old Harry?