Why will numbered lists not continue between documents in a book?

Dear InDesign community,

I am nearing completion of a 1100 page volume, organised as a book in ID CS6 (OS X) consisting of about 15 different documents. As per the excellent guidance in these discussions, I have used a paragraph style to generate figure legends via numbered lists.

For some reason, the numbered lists restart between the sequential chapters in the book, whereas I need them to continue between specified blocks of documents. Please note that I have already:

1. Set the numbered lists to continue from previous documents
2. Gone Type >> Bulleted & Numbered Lists >> Define Lists >> Edit List to verify that the "Continue Numbers from Previous Document in Book" is checked
3. Synchronised all documents in the book and updated numbering via the Book panel
4. Read lots of discussions on this site to try and locate this issue without success (but if you have a lead, I'm most eager to see it)

Any suggestions would be welcome; I have set things up by the proverbial book and it seems that simply checking the "Continue Numbers" box should be enough, but it isn't.

Many thanks for your assistance,

S.