Interesting discussions. If I trimmed up my mares feet she would probably be a good solid 40 &1/2". This is measured with my aluminum mini horse measure stick with a level built in with the mare standing on my concrete barn aisle.
I prefer smaller sized minis and bought this "38inch" mare only because she is just so gorgeous and her known bloodlines have heights that are 32, 34, 33.75, 37.25, 32, 33, 31.75, 33.5, 30.5, 32, 36 inches. I thought, when bred to the right small stallion I could improve conformation in my smaller size breeding program. And, add some black and buckskin color. I would not have bought her had her height been an honest measurement so I guess that means if there was on "over" breeding division I would not buy offspring from that either seeing even the known divisions are kind of a crap shoot anyway. To me, that is why it is called the "art" of animal breeding.
I don't mind that minis are not measured at the withers. The last mane hair seems to be a compromise or average (difference?) of the withers and the back. Then you would have the debate as to exactly where the withers start.
I am disappointed with the original breeder who kept this mare for 7 years, raised her and bred her, registered her and her offspring and then sold her last year as a 38" B. This Breeder, in my state, asked a nice sum of money and received it, according to the person I bought the mare from.
Aside from the extra few inches, this mare is just wonderful. My whole family loves her. My little minis do too because she is bigger and needs more to eat so they get to steal some scraps! LOL