aftertime vs posterity

aftertime

noun
  • A later time; the future. 

  • The process in which a harmony singer or background singer repeats a line or a series of words in a song separately after the lead singer rather than singing it in unison with the lead singer; prominent in country music and Southern gospel. 

posterity

noun
  • All the future generations, especially the descendants of a specific person. 

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