Further to Spencer Chase's reply on this subject, where he
describes use of strips of cloth to act as limiters to prevent
accordions stretching. For those instruments made by Aeolian in
London, use of tapes to prevent stretching was common practise.
My Duo-Art came with them, and I simply reused the old tapes.
See the photo (a slightly strange angle, as it's in the piano).

These were narrow cotton tapes, a regular product rather than
something specially-made. Aeolian used their favourite tacks to
hold them in place. Clearly, the tape must be fixed to each board.

If using pouch leather for the accordions, it should be sealed.
Because the accordions work using pump suction stiffness is not
an issue. I used the traditional approach -- egg-white -- but
thinned latex solution or acrylic glue would do just as well.

Julian Dyer

 [ https://www.mmdigest.com/Attachments/20/10/29/201029_011832_Duo-Art_accordion_with_restraining_tapes.jpg