Thanks to all for your excellent help. I have now worked out the Excel end of the process - it required several steps and IF... THENS, but it produces a usable list of pages for each author at the end. What I did in the end was to use a formula to check when there was a new person in the author list, and then a formula to isolate the pages of each new author, and then a formula to format that list of pages.

But now there's the Word end of it... Mail-merge isn't built to do agile logic - at the moment, my Excel sheet uses a column to aggregate the list of each person's pages in a cell on the last line of their name (makes sense?), and where they have multiple pages, each individual cell above that list is left blank (still with me?). So I want Word to skip these blank lines, and only mail-merge lines which have data in this particular cell - which data is the formatted list of pages...

Phew! This is complicated - but at the moment we're having to cut and paste a few hundred emails each month, and if I can get this to work it'll have been an afternoon very well spent! Thanks again for any help.