That's correct, links in ID are absolute. Rather than making a copy of the book folder, use the Package command to gather all the assets and update links for placed content to the copies. This probably still will not work with inter-file cross-references or hyperlinks, however.
I've delayed my response here.
Been dinking around, trying things.
That's a smart suggestion, but the Package command will round up all assets into a nice compact folder structure ready for production. It's not really what I need.
I need to keep things as they are, fully editable and unaltered - my folder structure is carefully crafted as is, and I definitely don't need all the fonts dumped into a folder.
Here's what I'm doing now - I make a complete new copy of the folder structure in question. It includes all InDesign files and linked artwork, etc. Everything.
I then CHANGE the name of root folder of the folder structure I initially copied. This breaks all the absolute paths of the copy.
Then I open each InDesign file and the CORRECT links are still automatically found because it looks inside the new folder structure I just made by creating the copy. So all links get "fixed".
Thank goodness InDesign is far more intelligent about finding missing links than Illustrator.
This is the best solution I've found. It's not perfect, but nothing ever is.
Brilliant! Saved me a couple of days of work. I think you can mark this one answered! Many thanks!