On sale date from the publication date and the volume number found at the Catalog of Copyright Entries, Part 2, Periodicals, New Series, Volume 35, 1940, Number 2. Second class permit. Copyright number 449437.
Letters credit identified by Greg Theakston and later Harry Mendryk on the Jack Kirby Museum web page http://kirbymuseum.org/blogs/simonandkirby/archives/2369, 31 October 2008 (retrieved 15 December 2014).
According to the Who's Who, Paddock probably illustrated this story, not L. Bing, so art credits revised to reflect this. Walter Frehm is a pen name (and by-line) for several artists, including Frehm himself (who drew the Green Mask in 1939), Paddock (who drew the feature in 1940), and Louis Cazeneuve (who drew the feature in 1941).
credits from Jerry Bails' Who's Who.