Sorry, I've been reminded that I suddenly swapped from one thousand words mode to a single picture, which I assumed would explain the solution I found in the manual.
In the screen shot in my previous post, which I assumed would be self explanatory (though might not be for those who had overlooked this feature), is a view of the Multi-File Search dialog.
Once the initial search has been performed, if there are any results found or replacements made, they will appear in a Search Results window.
Thereafter, scrolling to the bottom of the "Search in:" box in the Multi-File Search dialog will show a new section "Results Browsers" and an entry "Search Results" which can then be checked to restrict subsequent searches to only the files which matched the "Find:" pattern in the initial search.
That means it's really easy to continue with further modifications to just that group of files, such as what I needed to do, update revision/build numbers on those files alone.
I still haven't worked out why I'd never seen that before, except perhaps that it was always at the bottom of a long list of previous "Search in:" locations that I'd not thought to scroll down and see.
I know better, now :-)