A MORE COMPLETE SOLUTION:
Thanks for this conversation.
I found a way to put text at the start of the Endnotes section (I put simply the single word “Endnotes”), and have that appear only on the first page, and not on subsequent pages.
This has worked for three pages of endnotes so far, so I’m confident it will work for an unlimited number of endnotes.
I formatted the Page Style for Endnote. Went to Header, turned Header on, unchecked Same content on left and right pages (which probably didn’t matter), unchecked Same content on first page.
I put the content that I wanted into the header of the first page of Endnotes.
Then I went back, edited the Endnote page style again, and made sure Auto-Fit height was checked, but Height itself was at the minimum (it wouldn’t go below 0.04").
Incidentally, I set the style for the “Endnote” title the same as my chapter headings (Heading 1), and adjusted the height above and below. So now it stylistically matches my chapter headings.
I left the headers for the subsequent pages blank. So now those pages go almost all the way to the top of the page.
To get the spacing for “Endnotes” to stick through TOC updates, I had to adjust spacing in the paragraph.
Done!