nitty-gritty vs paper trail

nitty-gritty

noun
  • The core or essence of something; the gist. 

paper trail

noun
  • A written record, history, or collection of evidence. 

  • Records left by a person or organization in the course of activities. 

  • Physical evidence of something that occurred in the past. 

How often have the words nitty-gritty and paper trail occurred in a corpus of books? (source: Google Ngram Viewer )