postscript vs preliminary

postscript

noun
  • An addition to a story, play, etc. after its completion. 

  • An addendum to a letter, added after the author's signature. 

verb
  • To extend (a letter or another document) with additional remarks. 

preliminary

noun
  • Any of a series of sports events that determine the finalists 

  • A preparation for a main matter; an introduction. 

  • A relatively minor contest that precedes a major one, especially in boxing 

adj
  • In preparation for the main matter; initial, introductory, preparatory. 

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