assignee vs middleperson

assignee

noun
  • one who is appointed to act or speak in place of another; an agent 

  • one to whom rights or property is being transferred 

  • one to whom a thing is assigned 

middleperson

noun
  • An intermediate dealer of any gender; a middleman or middlewoman. 

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