PM vs post mortem

PM

verb
  • To project manage. 

  • To send a private message to (a participant in a chat room, etc.). 

post mortem

adj
  • Having been inflicted or having occurred after death. 

adv
  • Occurring after death. 

noun
  • An investigation of a corpse to determine the cause of death. 

  • Any investigation after the conclusion of an activity, particularly when said activity produces an unwanted outcome. 

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