From Denemo - Free and Open Music Notation Editor

     * the field y of each note caches the y-position of the notehead,
     * the field highesty of a chord caches the field y of the highest
       pitched note (ditto lowest)
     * the field stemy of a chord holds the y-position of the end of
       any stem the chord might have
     * the field is_stemup of a chord caches which way the stem should
       go (which changes with change of clef)
     * the field is_reversealigned of a chord caches the head
       x-position (left/right) relative to the stem.

The DenemoScore structure caches

curmeasure_stem_directive (set in calculatebeamsandstemdirs() as well as in a side-effect of the draw routine.)
curmeasure_clef (caches the value prevailing at the *end* of the measure??)
curmeasure_key
cursortime1,2
cursorclef

Some functions that would seem to be renewing cached values:

calculatebeamsandstemdirs() called inter alia by the ubiquitous displayhelper()
reset_cursor_stats()
newclefify()