Sue vs Tiff

Sue

name

  • A diminutive of the female given name Susan and of related female given names; popular as a middle name. 

noun

  • A Mary Sue (type of character in fiction). 

Tiff

name

  • A diminutive of the female given name Tiffany. 

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