proof sheet vs proofreading

proof sheet

noun
  • A page of proofed text; a sheet used to make corrections, emendations etc. before being printed for use. 

  • A contact print. 

proofreading

noun
  • The act or process by which a document is proofread. 

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