In the back side of the curve, basic longitudinal stability is still the same.
It is speed stability that becomes less and less stable and then in the back of the curve becomes slightly unstable, and then more and more as you get into it.
To my knowledge, most jet airliners have VREFs in the backside of the curve, but only slightly. That is why sometimes, with manual thrust, if you see speed decaying and take too long to fix it, speed decays more, and then you add some more thrust, but if you are too slow it is not enough and in this way you can end up with maximum thrust and still some knots below VREF. It is because of that speed instability. The way to fix that is to promptly add enough thrust to reverse the trend. THen the instability will play for you.