[cyberbaffled]

Here's the resolution of this problem: (1) there's no tag with the id="start" required in the bookname.html file; (2) if what's sought is the book opening in Kindle Preview at the location "_RWtoc-0" plus one menu item for that location in the "GO TO" menu, then there should be one reference element in the .opf file "Guide" section with this form: <reference type="text" title="" href="filename.html#_RWTOC-0"></reference>. This reference element results in the GO TO menu item "Beginning" being the same as the book-open location. If a "title" is specified -for example, Start Here- then the GO TO menu will include a "Start Here" item which specifies the same location as the "Beginning" item;
(3) if additional GO TO items are wanted, then what's required is .opf file Guide elements with the form: <reference type="anything" title="anything" href="bookname.html#anything"></reference>. The presence of a Guide element of type "<reference type="toc" title="Table of Contents" href="toc.html"></reference>" is entirely independent of the above considerations. Of course, it adds a TOC element to the GO TO menu. If the Kindlegen or Kindle Publishers guides say anything other than this, they're mistaken.