If I had to guess, they would do what was described in the article and try to descope (or better scope / negotiate) the question in a way they could answer with the tools they had.

With a targeted question, and the Dewey decimal system or similar, you should be able to find a source for most reasonably scoped questions within 5 minutes.

In a huge library, just the time it would take to physically hunt down the sources (providing they weren't checked out), would eat up some portion of that unless you're actually running around. I'm surprised they didn't ask for a phone number and call them back, but that would have meant the library paying the phone bill back in those days.

Reference areas were (and some still are) situated near tremendous libraries of reference books (like Encyclopedias, telephone directories, almanacs, etc.) and those were usually sufficient to address many of the types of questions the author lists. If you ever go to a rare book library, like the Lilly at Indiana University, the Beinecke at Yale, etc. (which you can visit for free!), the old school rare books librarians are still adept at using their reference books to answer questions pertaining to their trade. Those reference books are also highly sought after by said librarians and other book collectors.