One of the peculiarities of scores is the uniform title (240 field). Many of them are generic in nature (e.g., Symphonies, Lieder, etc.), while others have specific titles by which they are known (e.g., Messiah, Zauberflöte, etc.) In adding a work mark to the Cutter of the call number, use the 240 field uniform title and not the 245.
Some elements of the uniform title:
‡a : the generic music form or the specific title in its original language
‡n : the opus number or catalog number
‡m : the medium of the performance
Order of media:
Keyboard instrument (piano, harpsichord, etc.)
Other instruments in score order
‡o : the arrangement of the music
‡p : the section/part of the complete work contained in the score
All of these, in different ways, could determine the Dewey number and/or the Cutter number.