earlier vs heretofore

earlier

adv

  • previously; before now; sooner 

adj

  • occurring previously 

heretofore

adv

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

  • Previously within the present text; earlier herein. 

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