As for 1, someone might have thought that, but surely not the people who made concertinas, who should have understood how they work. In a stringed instrument, energy is put into the strings by bowing or plucking, some of that energy passes to the soundboard, and the soundboard couples some of it to the air. But in a free reed instrument the movement of a reed into and out of its slot produces pressure variations in the air, i.e. sound, directly. The baffle can then only reduce the sound. It may reduce some frequencies more than others, and that may be desirable, but it surely cannot help to send sound out. The only somewhat analogous thing on a stringed instrument would be a mute.