Even classical choral music gets tweaked by sucessive musical directors.

Although the notes don't get changed, the tempo, the phrasing and the dymanics are often different from rehearsal to rehearsal!

It's interesting that in my experience, most classical choral singers cannot sing without the music in front of them, even if they know the piece inside out. They find it hard, if not impossible to harmonise a tune unless it's written out for them. Many classically trained musicians are the same - they find it hard to improvise or fly without the dots.

LTS