Let's say someone has a box full of sheet music for solo piano to give away, and they invite you to rummage through it and take what you like. if you wanted to let them know how many pieces you took, how would you express that? "I took 25 pieces" doesn't quite hit the mark, since 'piece' in music is, I think, subtly more equivalent to 'opus' than to printed music.
'Manuscript' isn't right, since that refers to an original, not one of several reprinted copies.
If I were rummaging through a box of orchestral music I could say, "I look 25 scores," and the person would know exactly what I meant.
Is there a better word than 'piece' here?