Like you said, the declas-on-the-spot authority (or classify eternally) is the smoking gun. I also think this proves the Palpatine’s Revenge chat as legit.
I found that chat to be credible on its face. Reads very much like a sort of "check in, status report" exchange between people who know each other.
Very similar to Journ-O-List activity, except operating from a different vantage point.