I have to add that some ( surprisingly not all) concertina tutors do mention the importance of bellows control BUT mostly just in general terms like "the bellows is the soul of the squeezebox" or "use the bellows like the bow of the violin"...but without much analysis of the practical aims and means for it.Allan Atlas ( for the English system) tried to some part to reawaken the "Victorian" approach of Regondi and others but it is possible to go much further than that. Alsepti ( or maybe firstly Lachenals) introduced the notorious "bowing valves" but maybe they just made things extra complicated...