I'm sorry vs say again

I'm sorry

phrase
  • Indicates that the speaker is confused or requests information to be repeated; come again?, say again?, I beg your pardon?; see also Thesaurus:say again 

  • Indicates the speaker's commiseration. 

  • Indicates the speaker's apology. 

say again

phrase
  • "What did you say?" or "Repeat what you have said." A polite formula used when one has not heard or understood what has been said. 

  • To repeat part of or entire message transmitted over the radio, used instead of "repeat" which is an artillery procedure word. 

How often have the words I'm sorry and say again occurred in a corpus of books? (source: Google Ngram Viewer )