This is one of those questions that is sure to bring vast numbers of
opinions.  In all I have read, I can't recall ever seeing any original
instruction on how to store tune sheets for your music box but there
must have been some instructions at one time.

By observation, I have personally seen "Stella" sheets laying flat in
a drawer located in the base of a table model instrument.  I have a
17-inch Stella console player with vertical bins for the tune sheets.
Of course, with the Stella system there are no projections, so it
really does not matter how you keep your tune sheets as long as you
don't crease them. I have yet to see any warp caused by vertical
storage.  Edge damage can happen if you are not careful.

I have an early furniture plan book showing several models of floor
stands for your music box, some with vertical and some with horizontal
storage space.

The large 27-inch Regina instruments I have personally seen have had
both vertical bins with the tune sheets resting on their edge, and on
some, a rod where the sheets can be slipped over and hung from their
centre hole.

This is just my personal opinion, but I would always place the tune
sheets facing the same way so the projections faced the flat side of
the next disc.  This way, no projections from one sheet would get
snagged on the facing sheet becoming bent or broken off.  This position
also allows air circulation which is most important to avoid rust and
corrosion.

I would _never_ place any sort of padding, cloth, fabric or paper
between tune sheets.  It will attract moisture and cause rust to form
on the steel.

One final comment from personal hind sight: _never_ handle your tune
sheets with your bare hands.  A large number of my 27 inch Regina
sheets have a horrid mess of rusty but perfect impressions of full
finger and finger tip grab marks, around the edges where I touched them
with bare hands to remove or replace them from the storage bin when
changing the music on the player. It took a while for the rust marks to
develop and be noticed.  Once I saw what I had done, it was too late!

It is a lot easier to slip on a pair of white cotton garden gloves than
clean rust off your tune sheets.

Best to all
Ken Vinen - Stratford, Ontario, Canada.