I do not know what composers of the past would have used or written for concertina, or free reed instruments generally, but I have my own ideas on the matter; I am sure Haydn would have written a tune or two [perhaps for a royal dignitary commission].. and Telemann would have definitely had a go [and he would have wanted to play one too!]..
But then I thought the dynamic possibilities of concertina would be intriguing to Mr. Vivaldi..
So I had a go; and it was fun too! [Make of it what you will].. but improvising makes a pleasant break from more academic stuff.