I'm more forgiving of anachronistic steam engines or WWII bombers; it can't always be easy to get your hands on the right ones, even if you do care. I just find it odd that if a director says to a fiddler, 'We need you to play a lively tune for scene in a movie set in 1800', the fiddler wouldn't ask himself what tunes might have been around in that era. I doubt it's the director or the music director who's choosing the specific tunes, in most cases.