The Catalog of Copyright Entries, Part 2, Periodicals, New Series, Volume 35, January-December 1940, Numbers 1-4, lists this as volume 1, the date of this issue as January 1940 with a publication date of December 22, 1939, which is quite a few months before this issue's actual date. Second class permit. Copyright number 440219. Could be a publication error or perhaps an ashcan submission to the Copyright Office.
The on-sale date is from the publication date recorded in the Catalog of Copyright Entries, Part 2, Periodicals, 1940, New Series, Vol. 35, No. 2. The date of the issue is given as May 1940 with a publication date of March 15, 1940. Copyright number B449440.