On sale date from the fanzine, Fantasy News, dated April 14, 1940 (on page 3). The comic was scheduled for release during the week of April 14-20, 1940. Information shared by Bart Bush through the Comics History Exchange page on Facebook (4 October 2016).
Publication date of 25 March 1940 was reported to the U.S. Copyright Office and found in the Catalog of Copyright Entries, Part 2, Periodicals, New Series, Volume 35, 1940, Number 2. Copyright number B 451091.