Okay, so here's the work-around steps summarized for future reference:
Basically, if you want your Endnotes at the end of a section (NOT the end of the book; the index, etc. needs to go after it) and numbered from 1 to X by chapter, you have to do it manually. (I mistakenly thought the old 3.2.0 version of Open Office did the autonumbering of Endnotes correctly, but I was wrong. I saw that I did it manually back then, too.)
So instead of choosing Insert>Endnote>Numbering>Automatic, you must choose Character and manually type in the number of the footnote. (See attached) I recommend doing this after you're all done editing, and then going back and numbering them in sequence through each chapter. I usually do anywhere from 250-500 notes, so it's arduous, but it's the only way that seems to work and publishers will not accept "run-on" numbering of endnotes (i.e. 1-576 consecutively through the document). There is no "automatic" method that will renumber the Endnotes 1-X by chapter.
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[color=#FF0000][i]NOTE: The bug about the above methods is that footnotes disguised as endnotes can only be collected at the very end of the document. Endnotes can be collected at the end of a section so you can add other material after it, such as indexes, etc. but footnotes cannot. This is bad for authors, who need to add other material such as indexes at the end of documents AFTER the notes. Publishers will NOT accept this. So you have two terrible choices to make, and publishers will NOT accept either of them: Endnotes that won't allow you to renumber by chapter, that DO allow you to use sections and place other material after them, or Footnotes disguised as endnotes that will renumber the notes by chapter per Heading 1, but will ONLY locate at the very end of the document.
Thanks again to all for their help. This has been aggravating me since 2013.
