It's likely this was classified top secret and SCI (sensitive compartmentalized information). SCI compartments are classified, which is probably what was blacked out. Otherwise, it may indicate a classified partner knowledge sharing program that is classified.

Sort of. Conventionally, it's the cover name of the information compartment. If we knew what that was, since we now know what it refers to because that's unclassified, it wouldn't provide an effective cover anymore.

Of course, that's still a bit silly. The CIA insisted they redact even the initials of the countries involved. Ridiculous. Well, country R is Romania, country P is Poland. There are two others, I think Country J may well be Jordan.

I think I would probably be completely OK with this report being leaked in its unredacted form, including names: I sadly doubt there's any other way justice will ever be done and these people will answer for their crimes against humanity.

On the basis of googling "top secret noforn filetype:pdf", it seems that the convention is for the redacted text to be some kind of source classification (eg. "SI" for Signals Intelligence or "COMINT" for Communication Interception.

I have no idea what it would be in the case of this report, but my guess would be that it was redacted to avoid ambiguity given that "Unclassified" is stamped next to it, rather than because the classification is itself secret.

The classification is not secret, but the intelligence sources themselves likely remain classified, including the identification of the kind of sources supporting the information in the now-declassified executive summary.

Even vague descriptions of intelligence sources are often treated as more sensitive than the information derived from those sources.

Perhaps https://en.wikipedia.org/wiki/Greystone_%28CIA_operation%29