Jimmy dorsey did not like what was then Selmer's new model of balanced action alto. He appealed to the Selmer company in France for assistance. They built 7 altos with "Super" keyboard layouts with the B and Bb on the left side for Jimmy and his band members. It is believed they discovered enough parts to assemble another 10-13 horns. They all had serial numbers in the 27,XXX range. In total, approximately 20 of these rare instruments were made. Most of those still in existence are in the hands of rare instrument collectors. In the last 20 years, USA Horn has had only one other true Dorsey model that could make available.