I'm still thinking the point is recognition, not hypothetical knowledge. Take trolls, for example. In DFRPG (and some other settings) they are Fae. But in the arguably most well known fantasy setting -- LotR -- they aren't. In LotR, they are quite definitely not weak to iron, but are quite weak to sunlight. The other biggest info source would be D&D, in which their major weakness is fire. Also 'wrong', per DFRPG.
Ogres in most settings are large humanoids, and not at all related to pixies. The Reaper and his fellow fetches looked like creatures out of horror flicks, and wouldn't be recognized by most as Fae, and therefore alergic to iron. Lily and Maeve look only as Fae as they choose to.
So if you see a guy with REALLY sharp canines rip the throat out of your best friend ... well, those that resist denial are going to immediately connect the dots to form the word 'vampire' and are going to think of things like stakes, fire, sunlight, garlic, etc. But Someone who sees a Troll is going to reach for a torch ... and find that it's not nearly as effective as their college DM led them to believe.