come again vs come back

come again

intj
  • Used as a polite farewell to a visitor, inviting a return visit. 

  • A polite formula used when one has not heard or understood what has been said, or to indicate surprise. 

come back

verb
  • To return to one's possession, especially of memories. 

  • To retort. 

  • To return to a former state, usually a desirable one; to become fashionable once more. 

  • To return to a place. 

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