Even if what you claim is true, it still backs my point that some more explanation is needed on why those conclusions can be drawn.
Regarding the argument itself, was the memo really "regarding" Noam Chomsky? It reads to me like it's about some other people traveling to Vietnam, and the "with the endorsement of Noam Chomsky and Cora Weiss" is the only mention of him. Is it your claim that the mere mentioning of a person by name in a CIA memo means that there's a file on that person? Is there a copy of that memo in the files of all 8 people mentioned by name? If so, this expert should say that because it's relevant and interesting.
This is "large bureaucracy 101" and shouldn't need explaining:
1) The letter means the files existed.
2) The government said the files didn't exist.
3) The government lied (illegal) OR destroyed the files (illegal).
(1) is the part that I don't just assume is always true.
The "there's are names in a memo" => "there's a file on every person named" logic is something that, if true, would be nice to back up just a little, at least state why that's true for the CIA beyond saying it's true of all bureaucracies. (And I too have I've worked in large bureaucracies, including the government/military and with classified material)
Your argument seems to be that since the CIA is a large bureaucracy, that they have this hypertext-like system of filing copies of all documents in every file associated with terms in the document. I don't doubt that they _now_ have a system like this - they'd be silly not to. But in the 70's? That's, like I said, interesting and relevant if true. And it'd be nice to at least have the expert say "Yes, this is how the CIA managed documents in the 70's based on (CIA statements | my investigations | interviews | etc)."
I'm not saying that the CIA didn't have a file on Chomsky, it would surprise me if they didn't, but that jump from mention to file deserves a little more treatment.
My experience of bureaucracies dates back to the mid 80s when nothing much was (in Australia) computerized. I'm not talking about a "hypertext-like system of filing" but a physical room full of hanging folders with unique numbers and index cards. (You've seen images of the -- newly added! -- file compactuses* at the Department of Veterans' Affairs -- like that.)
* Not a typo: compactus is a specific piece of furniture.
If a letter primarily concerning X gets sent, a copy of it is retained in the file on X, and the receiver puts the item in another file on X. If necessary, multiple copies are retained and placed in multiple files (e.g. the letter also concerns Y so photocopy it and insert it in files on Y).
Each page in a file is numbered (this is called a "folio number") and the file's folder is amended to show the new inserts and increased folio count. It's hard in such a system to lose a page and very hard to erase evidence of its prior existence.
Typically, multiple index cards (e.g. "Chomsky, Noam -- file 12345") will get created for each file, and inventory will be taken of all files, folios, and index cards on a regular basis. Destroying a file or folio creates visible gaps and broken references, so it's actually a pretty robust system. Yes indeed, this is how this crap worked before computers.
Regarding the argument itself, was the memo really "regarding" Noam Chomsky? It reads to me like it's about some other people traveling to Vietnam, and the "with the endorsement of Noam Chomsky and Cora Weiss" is the only mention of him. Is it your claim that the mere mentioning of a person by name in a CIA memo means that there's a file on that person? Is there a copy of that memo in the files of all 8 people mentioned by name? If so, this expert should say that because it's relevant and interesting.