> Say your text has a body with several pages, some formework which spreads
> over facing pages, and - to boot - a footnote which starts on one page and
> ends on another. How many <pb/> would you use?
One pb at each place any textual constituent continues on a new page, whether that is the main text, a note, formework, an inset, or whatever.
> Sounds like a job for (currently nonexistent) <nb> ("note break").
A note can continue on a new page, but also in a new column, or even in a new gathering. We don't call a pagebreak in a chapter a chapter break. So why call it a notebreak in a note?