When Stamps are issued in sets on the same date or on the same topic at different but close dates, they are sometimes printed on the same sheet to form a Compound Deluxe Sheet. Compound Deluxe Sheets, also called Collective Deluxe Sheets, are much scarcer than regular Deluxe Sheets as only about twenty-five of each issue exist. Until 1940, some Deluxe Sheets were issued only in compound format, and although they are now very rare, more than twenty-five copies were printed.