Walt,  To answer your questions in order:  There were 4 rolls in the
set and they came packaged in a black box that looked like a shoe box.
There  was an instruction book and several little tags with strings
that were to be fastened to the controls on the piano.  I had a
complete set that I sold several years ago.

Other MMDers report that they have seen these sets so they are not
terribly uncommon.  As for completing the set, you are more likely to
find the complete set of rolls than individual ones, but anything is
possible.  The book and tags are most likely to be missing from any
set.

As to usefulness, they could be generally used for other brands of
piano as most had essentially the same control functions.  The
specifics would vary as some pianos used levers and others used buttons
for some of the functions such as soft treble/bass and sustain
functions.

Unless a roll is totally unused, you will probably not hurt it by
playing it so I would go ahead and try the ones you have.  You may
decide that it is not worth the effort to find a complete set or to
complete your own set.  Or you might like it.  That's for you to
decide.

Gulbransen was not the only one to issue instruction rolls although
they seem to be among the more common.  QRS, among others, also issued
instruction rolls.

To clarify my previous comment about an unused roll, sometimes you will
find a piano roll with a sealed box.  Sometimes, as with Ampico rolls,
they originally came with a paper seal wrapped around the roll.  In
these cases, I might be reluctant to break the seal just to play a roll
especially if the rest of the box looks mint.

I would be interested to hear if others agree with this or if there is
little collector value to an unused roll.  I have at least one like
this in my collection.

Hope this helps,

Bob Conant
Endicott, NY