How did scholars produce dissertations when specific texts may not be readily available? Flipping through books is one thing, but it's much easier when one can get the book he needs quickly if it is not online.
I wrote a bit about how to do academic research before the Internet in an earlier thread.
In general they did plan ahead more. But interlibrary loan is very old, and the library can get you just about anything you need (books, articles and theses) if you can but wait 2 weeks.