red-letter vs usual

red-letter

adj
  • Particularly significant or positive. 

usual

adj
  • Most commonly occurring; typical. 

noun
  • A specific good or service (e.g. a drink) that someone typically orders. 

  • The typical state of something, or something that is typical. 

How often have the words red-letter and usual occurred in a corpus of books? (source: Google Ngram Viewer )