incidentally it looks like that code requres  $cite-ref to be a single
element node, but you have declared it as

<xsl:param name="cite-ref" as="element()*"/>

ie you allow it to be the empty sequence or more than one element.

Yes, I think I had a comment there that indicated I originally defined it as just element(), but in one case (when I was formatting an entire book manuscript), I got an error about an empty sequence. Am not sure how that's possible in this case ...