junior varsity vs third string

junior varsity

noun
  • In sports, a team composed of players who play behind the varsity unit. 

third string

noun
  • A unit of players that plays behind the first and second strings; a junior varsity team. 

adj
  • Of a decidedly lower quality or condition. 

How often have the words junior varsity and third string occurred in a corpus of books? (source: Google Ngram Viewer )