Regarding your statement:
That's why you should always use keyrefs for all references to topics (and anything else).
I'd like to understand how far to take this.
Some of our books are many thousands of topics. Should I assign unique key values to every topic in the bookmap? Or should I only assign key values to referenced topics? Should we require writers to define key values (in addition to filenames) for every new topic they create? I could repurpose filenames as key values too, except there will be collisions of same-named files in different directories.