backdate vs misdate

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. 

misdate

verb
  • To date incorrectly; to mark with the wrong date. 

noun
  • A wrong date. 

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