My immediate reaction when I first saw the innards of one of these
fan accordion systems a year or so ago is that the regulating valve
appeared to be identical (not just vaguely similar) to the curtain
valve that Hupfeld used to control accompaniment levels in its later
Phonola player pianos.  This is a curtain valve, a sheet of leather
that is pulled aside to modify the air flow.

Underlying both Hupfeld and Aeolian players was use of a Theme system,
the 'snakebite' perforations in the rolls, and presumably some form
of licensing or sharing agreement existed.  It's not impossible that
something of the sort occurred in the 1920s when Hupfeld introduced
this new form of regulator.

It would be interesting to do a direct comparison of the fan expression
system with a Hupfeld regulator.  I suspect that the latter are
distinctly uncommon in the US, although some may have been used in
fancier and more complex instruments that shared some piano components.

Julian Dyer