Just noticed this thread for the first time and got the impulse to send some piece of exotic information. Unless someone objects I believe that the most long lasting concertina band in "our own time" i e the period after the old bands like those mentioned by Alan Day in the primary message to the thread in 2007 has been "my" band of the The Swedish Concertina Society - SCS.
It was started 1981 by a group of 10-12 players within SCS which at the time had about 30 members. From 1990s and until 2012 when the last member except myself passed away we were 4-6 active players.No proper recordings were maid ( sadly since we believed the interest would be too poor) Just a couple rehearsals were saved on tape. We used to have concerts 2-4 times a year in the Stockholm region and for 30 years we met regularly ourselves every 3rd week.I am still keeping the instruments and all the arrangements and I will gladly answer any questions about the inspiring experience.