Thanks to Jason and others for all advice I have so far been given on this thread.
Over the weekend, my lengthy contacts with Apple advisors have led me to the conclusion that it would be a good idea to re-migrate from my old 2011 MacBook Pro to my current 2018 MacBook Pro (after having ’nuked’ the 2018 disk, as the advisor puts it, to ensure a clean start), thus hopefully eliminating any problems that may have arisen with permissions as a result of any imperfections in the earlier migration process.
If I am lucky, the result of that should be that I end up with Word 2011 and Endnote working harmoniously again. We shall see!
Because I am travelling, I shan’t be able to do the nuking + new migration until I am back near my old machine in a week’s time. When I have carried out that process, and hopefully have a pristine clean and permissions-perfect installation, I shall return and report the result.