grist for the mill vs worthiness

grist for the mill

noun
  • Something that is useful or that creates a favorable opportunity. 

worthiness

noun
  • The result or product of being qualified or eligible. 

  • The state or quality of being qualified or eligible. 

  • The result or product of having value or merit. 

  • The state or quality of having value or merit. 

How often have the words grist for the mill and worthiness occurred in a corpus of books? (source: Google Ngram Viewer )