It appears that there were problems with rubber cloth even in the
1920's.  Many years ago I restored a Steinway grand; it had never been
touched.  Upon removing the pneumatic stack, I discovered about 60% of
the striker pneumatics were in excellent condition, the other 40% were
dried and cracked.  You could actually see where the quality stopped
and continued onward with poorer quality rubber cloth.

I assume that someone covering the pneumatics ran out of rubber cloth
and started using cloth from a different batch.

Bruce Clark