That does not quite fit-- As I understand it, the rules concerning active classification require all information about active agents to remain secret, and redacted. They cannot become "unclassified" until after these agents stop being active.
Now, maybe there are "inactive" spies in Russia, who are now "improptu informants", who used to be active spies, then the soviet union collapsed, and they just kept living there, and they send useful intel every so often through unofficial channels. I could see the 3 letter agencies wanting to protect these people, because they will be prosecuted as if they were still legit active spies, instead of just volunteer moles. (espionage law does not have a loophole for "I totes did it for free yo, so you have to let me go", and the reincarnation of the KGB is just as ruthless as its cold war incarnation.)
More than likely, I suspect that rather than protect agents, (which again, would not require extension to keep classified), it contains information that is unflattering to the 3 letter agencies involved. Unflattering could be anything from "shameless mishandling", to "Yup, we totally killed that fucker for wanting to stop that war." in this case.