occur vs prove out

occur

verb
  • To come or be presented to the mind; to suggest itself. 

  • To happen or take place. 

  • To present or offer itself. 

  • To be present or found. 

prove out

verb
  • To turn out to be feasible, accurate, true, satisfactory, as expected, hoped, stated, etc. 

  • To demonstrate the feasibility of; to show or be shown to be feasible, accurate, true, satisfactory, as expected, hoped, stated, etc. 

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