Considering how much her lungs must be constricted its not a record I would encourage anyone to aim for. It looks a painful thing to endure.
Cathie Jung (USA, b. 1937) has a corseted waist measuring 15 inches. Un-corseted, it measures 21in. Her enthusiasm for Victorian clothes is why at the
age of 38 she started wearing a training belt to gradually reduce her then 26in waist. She has never had surgery to define her waist