garden apartment vs servants' quarters

garden apartment

noun
  • A detached mother-in-law apartment or cottage on the same parcel as the main house. 

  • An urban apartment in a multistory building located at or below ground level. 

  • One of a set of low-rise apartment buildings built among landscaped grounds and often arranged around courtyards that are open at one end. 

servants' quarters

noun
  • A mother-in-law apartment or garden apartment used for in-house employees 

How often have the words garden apartment and servants' quarters occurred in a corpus of books? (source: Google Ngram Viewer )