Dan, I was asleep when I suggested that the tubing was displaced!
Your explanation of the early Duo-Art split at E/F, as in the
Ampico, is quite plausible.  But the date of the incident (1914 or
earlier) suggests yet another possible explanation:

Mr. Charles F. Stoddard, the Ampico inventor, held several key
patents used by Duo-Art, including, I believe, the patent for the
accordian-pneumatics used for expression control.  One can imagine
that Aeolian "hated his guts", but they were powerless until the
merger of the two companies in the 1930s, when - some say - the
Aeolian management ordered all the Ampico perforators thrown in the
river!

Is it possible that, among all the other patents, Stoddard held a
patent covering the E/F stack split in a reproducing piano, and that
he refused to license it to Duo-Art?

-- Robbie Rhodes