petty theft vs pilferage

petty theft

noun
  • A theft of property having a value lower than a certain small amount set forth in a statute, and considered to be a less serious class of crime. 

pilferage

noun
  • The individual act or recurring practice of stealing items of low value, especially in small quantities, for which the legal term is petty theft. 

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