The NUMWORDS field takes no range/bookmark or Style arguments. You could use a formula field to deduct the word counts for your 'exclusion' content, but you'd still need to do a word count of all of those ranges. That becomes quite involved when, as your post suggests, you only want to exclude parts of your references, headings, & citations.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]