but even when he was unnamed, the Guardian had piles of hard evidence to back up the 2012 Pentagon stories.

I guess to me, the difference between publishing some documents [1][2] or slides [3] as per your example with The Guardian isn't that different (again, for me) as implicitly saying "the source(s) is/are legit" if whoever's publishing the information has a track record of being trustworthy regarding factuality since I can't necessarily verify the authenticity of that evidence anyway.