Tunesmith: I really don't understand your position. If Bessie Smith starts a note say a semitone "flat" of what you think it ought to be, slides up to a little above the "correct" pitch, and then settles back to a note just below the "correct" pitch, are you saying she is singing out of tune. And if so, at which point of the slide is she out of tune?
Of course, some players can't manage to play or sing what they are aiming at, and miss it by so far that it is agonising. That is obvious. But it seems to me that Tommy Jarrell, for one, does pretty much what I want him to ie sound bloody marvellous.
What on earth do you make of those strange Kurdish and Arabic scales?