pony keg vs superette

pony keg

noun
  • A drive-through liquor store; by extension, any convenience store. 

  • A container for beer holding 7.75 US gallons, equal to half the size of a standard beer keg. 

superette

noun
  • A convenience store. 

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