The only mistake I can see happening is if the DM somehow thinks that it's impossible for a PC to ever truthfully assert that s/he knows or recognizes the name of an NPC.
You're reminding me of a thread from...a few years ago? An anti-metagamer offered a scenario in which werewolves simply
didn't exist in a game world, until of course the DM decided to bring one in. "How," this poster argued, "would it be possible to have any knowledge of werewolves and their vulnerabilities?"
On the one hand, this raises the question of what "reality" is in a game world (as per my comment up thread). Does that reality exist independently of what has been experienced by the adventurers? Does the DM actually control every aspect of it? After all, if a werewolf suddenly exists in that world, it came from..."somewhere". Right?
On the other hand, werewolves
don't exist in our world, either, and yet somehow even non-gamers know that you need silver weapons to kill them.
This recurring debate about playstyle, and the insistence of the anti-metagamers that we are not only doing it wrong, but "cheating", keeps making me think of the movie, "Lords of Dogtown". Specifically, the scene where Tony Alva, Stacy Peralta, and Jay Adams show up at a skateboarding competition. All the other competitors were freestyle skaters, the style that basically defined skateboarding since the 60's. They took umbrage at these newcomers using skateboards in a way that one just simply did not do. They weren't following the rules. They were defying tradition. They were
cheating.
And, of course, what these newcomers were doing was freakin' awesome.