Subject headings are honestly overrated and people act like they are some magic key when they are just someone else's guess at what a book is about. Half the time the headings are outdated or weird, like everything gets tagged with five terms that have nothing to do with what you actually need. A librarian can type two words and find cool stuff because she knows the collection and the database quirks, not because subject links are some secret hack. Search by keyword, then sort by date, and you will find the same oral histories without playing follow the link for an hour. The real trick is asking a human who works there, which is what actually happened in your story.