countersignature vs superscription

countersignature

noun
  • A signature made to confirm or endorse another. 

superscription

noun
  • Something written (or engraved) on the surface, outside, or above something else; specifically, an address on a letter, envelope, etc. 

  • An editorial addition at the beginning, often indicating the authorship of a piece. 

  • The act of superscribing. 

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