libretto vs manuscript

libretto

noun
  • A book containing such a text. 

  • The text of a dramatic musical work, such as an opera. 

manuscript

noun
  • A single, original copy of a book, article, composition etc, written by hand or even printed, submitted as original for (copy-editing and) reproductive publication. 

  • A book, composition or any other document, written by hand (or manually typewritten), not mechanically reproduced. 

adj
  • Handwritten, or by extension manually typewritten, as opposed to being mechanically reproduced. 

How often have the words libretto and manuscript occurred in a corpus of books? (source: Google Ngram Viewer )