coverlet vs duvet

coverlet

noun
  • A blanket used as a bed covering, usually quilted. 

duvet

noun
  • A quilt or usually flat cloth bag with a filling (traditionally down) and usually an additional washable cover, used instead of blankets; often called a comforter or quilt, especially in US English. 

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