add insult to injury vs cap it all off

add insult to injury

verb
  • To further a loss with mockery or indignity; to worsen an already unfavourable situation. 

cap it all off

verb
  • To surpass or outdo something. 

  • To finish or complete something; to add a finishing touch. 

How often have the words add insult to injury and cap it all off occurred in a corpus of books? (source: Google Ngram Viewer )