the text:note-ref element has the attribute text:note-class.
the text:note-ref element refers to a text:note element by the text:note's text:id attribute.
the text:note element already has a text:note-class attribute.

this duplication would only make sense if the text:id namespace for
text:note elements were defined per note-class, which i would find
highly surprising (e.g. if you could have a footnote with text:id 42 and an endnote with text:id 42 as well).

if footnotes and endnotes share the same text:id namespace (i.e. there cannot be a footnote with text:id 42 and an endnote with text:id 42 as well), then the text:note-class at text:note-ref is completely redundant, and can be removed.