backdate vs forerun

backdate

verb
  • To give or assign a date to a document that is earlier than the current or true date. 

noun
  • An assigned date that is earlier than the current or true date. 

forerun

verb
  • To precede; to forecast or foreshadow. 

  • To run in front. 

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