Some of the info out there, is a little too "deep" for the average runner to know I feel... (like that Dunkie killed himself)
So I basically play it by ear with my players... If once pulls out a piece of meta-game knowledge and doesn't have the skills to back it up, I say "No".
If they have to skills to back up... then I let it in....
But you are right, there is a fine line between player known, PC known, and runner Known... and it can be hard to tell them apart.