So, the underlying question here is: how much knowledge about vampires do adventurers or regular people in the forgotten realms have? Do they know their weaknesses (sunlight, running water, stake in the heart...), their reproduction mechanics, their feeding habits?
The reason I am asking such question is that I am currently running Curse of Strahd (5e), and the characters in my party were brought to Barovia from the Forgotten Realms. I was wondering how much they should know about vampires before going to the adventure. Being 1st level adventurers, they obviously never faced a vampire, but how likely is that they read books about it, heard about it in random tavern chitchats or obtained such knowledge in some way?
As an example of why this question matters: would it be obvious that a sun blade (especially the Sun Sword) is extremely useful against vampires (especially the sunlight property)? Would they think about bringing him or any other vampire to a river?
Note: To clarify, my intention is not, in any way, to stop players from using such knowledge. I am running CoS with a very open mind on metagaming anyway. I want to understand/know this because the adventure has a handful of situations where the characters are given such pieces of information, e.g. when the Tome of Strahd tells them he is affraid of the Sunsword. However, that knowledge is quite meaningless if the characters already knew/know that vampires, in general, are weak to sun blades, any way, and borderline useless if the characters already possess the Sunsword (so it doesn't even tell them the sword exists). So I was hoping that I could justify - at least to the players - that their characters are actually learning something new, although it is obvious to the players themselves.