More on the subject:

Thanks, Mike Kitner for sharing your recollections of the test roll you
made some years ago. I will take a drill index with me when I go back
to the piano (hopefully later in the Fall) for a precise measurement of
the 'go no-go' holes.

I agree with Pete Knoblock that the 'go no-go' idea would be a great
way to verify uniformity of note volumes. It would work wonders for a
straight player and be even better for a reproducer. One comment is that
all of the T-100 machines I have seen are all double valve stacks. I
haven't thought the implications through yet, but like the bumblebee,
it flies nonetheless.

There were no instructions on the roll about the purpose for the holes,
but I think that once a piano left the factory, having been adjusted
with this factory roll, then field adjustments would be pretty minor. I
know of a 1913 upright Mason & Hamlin T-100 that has never been rebuilt,
and although it shows the signs of it, still plays at mezzo piano and
above. It came from the factory here in the US and had been followed,
over the years by Otto Kremp. It had not been adjusted or  worked on
for 40 plus years, until last summer. I suspect the factory roll was
used to set it up.

I'm going to add this to my list of projects: making a copy of this
particular test roll, since it was from the hands of Welte himself.

Regards,

John McClelland