heretofore vs once upon a time

heretofore

adv
  • Before now, until now, up to the present time; from the beginning to this point. 

  • Previously within the present text; earlier herein. 

once upon a time

adv
  • A long time ago; at some time in the past (a traditional beginning of children's stories, especially fairy tales). 

How often have the words heretofore and once upon a time occurred in a corpus of books? (source: Google Ngram Viewer )