I looked again at the BibX example for partdesc (which is where my
partDesc came from).

Would this -- the ability to have composite references (the specific
details of how to name elements is less important) --not better
accommodate your example Suzanne?

          <single type="volume">3</single>
             <single type="part">1</single>
             <single type="part">3</single>

This was designed to be able to get a citation like:

Some Collection Title, volume 3, parts 1, 3.

The other example was...

     <single type="chapter">1</single>
     <range type="chapter">
  </partdesc> get:

Some Book Title, chapters 1, 3-5.

BibX, BTW, parses all start/end extents, including page numbers
(important for formatting processing).

The above doesn't solve your interest in including titles of course.