anachronism vs backdate

anachronism

noun
  • A chronological mistake; the erroneous dating of an event, circumstance, or object. 

  • A person or thing which seems to belong to a different time or period of time. 

  • The aberrant projection of the present onto the past. 

backdate

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

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

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