bookfell vs sheepskin

bookfell

noun
  • A skin prepared for writing upon; a sheet of vellum or parchment; paper. 

  • A vellum or parchment manuscript. 

sheepskin

noun
  • The skin of a sheep, especially when used to make parchment or in bookbinding. 

  • A diploma. 

  • The tanned skin of a sheep with the fleece left on, especially when used for clothing, rugs, etc. 

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