Just to add to this thread, organ builders I have spoken with often
iron the pouches in their jobs after dishing and gluing down.  This
guarantees that the edges of the pouches are sealed, and will remove
many of the wrinkles that may be formed initially.

A couple of precautions however.  The iron must not be too hot, the
pouches should have their centers pushed down into the well, so as to
avoid heating them with the iron, and an intermediate layer of material
should be used between the iron and the leather, to avoid the pouches
sticking to the iron and lifting off.

The results can look absolutely perfect with a little practice.  Of
course you cannot do this with glues that don't soften when heated.
But why would you even use such a glue?

Paul Morris