Different quality raw materials determine reed quality. There are many different shapes and systems of keyboards in accordions. This needs to be looked at from a historic perspective. The first accordions used buttons on both right and left hand and were mainly diatonic. As the accordion developed, accordionists' wanted more notes so chromatic systems developed both button and keyboard.
All systems have their good and bad points.
See Types of Accordions and How they Work for more detailed information. This is achieved by removing weight from either the tip or the base of the reed. There is no 'fixed' amount of higher or lower tuning to achieve musette. Accordions are manufactured in many countries. Most production takes place in Italy, Austria, Germany, France, Russia, Czechoslovakia and China.