Dear Vincent, Bonjour from The Bronx (N.Y.C., U.S.A.)!  I am quite sure
at one time there would have certainly been a "Primer", or coding chart
in the roll coding and editing departments of The Aeolian Company.
It would probably have had numerous editing or writings in the margins.
It would more than likely have made note of where and when a specific
bit of coding would be warranted, or where it would be most effective.
Probably even some of the more prolific (or in house) roll artists had
a copy of their own.

Back in the 1970's, there were still quite a few, but rapidly dwindling
numbers of roll artists still extant.  Some were even made Honorary
Members of AMICA, and/or other such noted organizations.  They would
mesmerize their audiences with wonderful anecdotal stories of how the
business was run (with a fair amount of "artistic license" thrown in,
I am quite sure).  A few may have even held workshops explaining the
ins and outs of roll editing.  We can only hope there was someone
taking notes or recording the proceedings.

One such artist resided not very far from me, right here in The Bronx,
but owing to my shyness I never approached her, even though on one
occasion I had been asked to do so.  (I now curse my blasted shyness!)
I regret having missed conversing with not only a very talented roll
artist, but a fantastically gifted pianist.

I am quite sure your explanation is close to being an accurate
description, and should there be anyone with a differing view, please
feel free to offer a dissenting opinion.

Sincerely,
Dale F. Rowe
Bronx, New York, USA