The Tornado rule is extremely strict (in many areas tolerances are a few millimeters or grams).
Therefore I think that the Tornado class deliberately omitted to include the mid girth rule after the revision followed to the 2000 Olympic Games.
Don't forget that Mitch Booth is the father of the "TORNADO SPORT".
From a performance point of view I consider the mid girth rule SILLY.
Most likely it was introduced by the founders of the F18 class.
For sure the first F20 rule (the one agreed in 1989 by Lallo Petrucci for BIMARE, Enrico Contreas for MATTIA & CECCO e Christian Favre for VENTILO) did not include this rule.
I remember that many sail-lofts such as Oxosails developed very nice code Os in a very light mylar cloth available at the time.
Since all we catsailors love to go faster and faster, I would let all the catamaran classes to test these new code Os.
If they prove to be faster than the existing asymmetrics then we should adopt them.
So all my praise to Mitch, Charlie, Jay and Pablo who dare to introduce this new weapon!
I am firmly determined to contact Ullman Sails immediately after the end of the Olympics to have one Code 0 made for my boat