Notes:
Joe Simon began editing for Timely on a freelance basis with Red Raven Comics #1, which came out the previous month. It is not clear if he immediately started editing Marvel Mystery Comics as well or not, although he was definitely the editor by issue #12 as discussed in that index.
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. 3.