regrade vs reoccur

regrade

verb
  • To regroup or reassign. 

  • To change the classification of (potentially secret documentation). 

  • To grade again, give a new grade or grading to. 

noun
  • The act or process of grading again. 

reoccur

verb
  • To occur again; to recur. 

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