I mean I do think it's a problem if you are say, watching Mad Men and in the final season everyone is suddenly vampires? If they didn't tip that off at some point?
But on the other hand I'd probably respect the hell out of that choice.
Sorry I have no context for this particular conflict.
the first season of Gangsters was this really realistic gritty 70s cop drama. the second season of Gangsters involved the gritty 70s cops fighting against a load of people with supernatural powers
the writer had been trying to make a point that 'Realistic' cop drama is not actually any less of an unrealistic power fantasy than fantasy. people hated it though and the BBC cancelled the show
I mean, I think it's an interesting question--there are ways to like, telegraph that "oh we're in a world where x/y/z is not impossible" but I think it's not a hard and fast rule how explicit you need to be.
one of my fav things of mgs2 (before mgs4 trying to retcon /almost/ everything) was how vamp would throw knives to your shadow to stop you from moving and that's it
But on the other hand I'd probably respect the hell out of that choice.
Sorry I have no context for this particular conflict.