[ Ref. https://www.mmdigest.com/Attachments/21/03/12/210312_022235_TB_88n_unknown.jpg
 

The tracker bar in question has a giveaway in the milled vertical
grooves above and below the note holes. They show the stack split,
a visual reference for the operator. So, it's a regular player
piano tracker.

Some makers chose to print a guide down the centre of rolls, but
here it was engineered into the system. The maker? Hupfeld.

The attachment is from the 1930 Hupfeld factory scrapbook. A slightly
different design (it's a Phonoliszt model), but the similarity is clear.
The whole book is in a PDF on Marc Widuch's website:

https://www.faszinationpianola.de/en/ 

When Aeolian came up with the now-standard 88-note tracker bar design
they chose 9-holes-per-inch to give margins for extra controls. (Others,
e.g. Melville Clark, argued for 8-per-inch which wouldn't have had
margins nor even all 88 notes! How lucky we are that such stupidity was
rightly ignored). And, like Phillips with the compact cassette and CD,
Aeolian gave licence-free right to use their design for both the tracker
layout and the roll chucks (spool ends).

The sustaining pedal was widely adopted everywhere, but the space left
for Theme-accenting ports immediately outside the note tracks was less
commonly used. In the USA the only maker who used them widely was Wilcox
& White, thanks to their patent-sharing agreement with Aeolian.

Outside the USA, however, Theme accenting was widely used, even by
makers such as Standard and Autopiano for their export models. So,
a tracker bar with Theme ports not known to be Aeolian/Angelus can be
assumed to be from a European instrument.

Julian Dyer