My local State library is an absolute beauty and has some uncommon features. It has a staff of fulltime specialist music librarians. It has many thousands of music titles and some hundreds of folk related titles, many of them with music scores. Best of all I can borrow quite rare books for periods of up to a month at a time.
If only I had more time to devote to research! I tend to concentrate on lost tunes, but in truth there are thousands of songs out there that are not chronicled on the DT. The task is endless. Regards, John