air buttons on English concertinas

[Mike Franch]

When did air buttons on English concertinas become common? I imagine that they first appeared on more expensive models and then perhaps worked down to less expensive ones, but this is a guess and it gives me no idea of the chronology. (By "English," of course, I mean the type called "English," not those made in England.)

[yankeeclipper]

My 1915 Wheatstone treble EC has slots in the metal ends for air levers - there is an air lever on the right side but not the left.