disclosure vs thank-you note

disclosure

noun
  • The act of revealing something. 

  • That which is disclosed; a previously hidden fact or series of facts that is made known. 

  • The making known of a previously hidden fact or series of facts to another party; the act of disclosing. 

thank-you note

How often have the words disclosure and thank-you note occurred in a corpus of books? (source: Google Ngram Viewer )