I just tried using auto-numbered headings with "unnamed" LISTNUM fields in the body text paragraphs and it doesn't seem to work - it tries to number as if it is next number of heading level.
It kind of works with LegalDefault, but there seems to be odd side effects if you have unnumbered paras in between.
Anyway, thanks for help - I will stick to { LISTNUM LEGALDEFAULT } at least for current document.
I think a built-in "body text" style that assumed the next level down from the previous heading level would be a good addition to word.