Hi David,
I opened every chapter/doc in the book, including the pages with the illustrations, and went back and recreated the hyperlinks making them point to the pages they should. Choosing the page automatically updated the page number, so I thought everything was working. In fact, I was certain you had the right answer because with all of the documents open their names showed up in the list of documents to link too, which wasn't the case when I'd first tried.
Unfortunately, exporting to PDF and then testing one of the links still gives an error “File not found”. More strange, it's looking for the full absolute path to where the file would be on the hard drive–but for the file name with a .pdf extension, as if it thinks the target should be the linked stand alone pdf document in the directory.
For some reason it isn't generating internal links pointing to the document location, or even the page number, inside the exported pdf itself. There must be something I'm doing wrong if you have any other ideas. I don't want to believe InDesign is so kludgy in something done all the time in html.
Thanks,
JTT