Generally speaking, in most international music copyright law of which
I am aware, if an arranger makes a new arrangement of a piece of music
on which the original copyright has elapsed, the resulting arrangement
becomes the sole property of the arranger.

You don't even have to have changed a note of the melody, or even have
re-harmonised the music, for this to happen; A change of context or (if
it is a song) the substitution of different words may be sufficient.

Offenbach died in 1880 and so his works have been out of copyright for
many decades.  The Gendarmes Duet may not actually have been out of
copyright when Holcomb adapted it (did he ask for permission, one
wonders?) but it certainly is so now.

I fully understand the importance of Thomas Holcomb in the history of
the United States Marines (having looked him up on Wikipedia); however,
it would be bad taste indeed to ignore the contribution of the original
composer, without whom the famous melody would not exist.  If there is
sufficient room on the roll label, I would put:

  (music) Jacques Offenbach, adapted by Thomas Holcomb

As has been discussed many times before in this forum, roll labels can
often be a bit sketchy, favouring publisher details over composer and
lyricist, for example, in the case of QRS.  Let's try and make new ones
as accurate as possible!

Greetings from the UK,

Rowland Lee