keepsake vs pro memoria

keepsake

noun
  • Some object given by a person and retained in memory of something or someone; something kept for sentimental or nostalgic reasons. 

  • Specifically, a type of literary album popular in the nineteenth-century, containing scraps of poetry and prose, and engravings. 

pro memoria

noun
  • A memory-aid; a reminder or memorandum, especially a book or document serving this purpose. 

  • A document circulated in a meeting or summit for discussion purposes. 

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