The blurb at the end of the story invites the reader to follow Flexo's adventures in the next issue of Daring Comics (note title mismatch - the feature remains in Mystic Comics).
Michael Vassallo, Jim Vadeboncoeur, Jr. and Hames Ware believe that E.C. Stoner may have assisted Binder on this, probably on inks and not pencils.
From the Chesler Shop.
Contrary to various other published theories including Who's Who and the Masterworks, "Harry / Douglas" was an editor/artist named Harry Douglas, as confirmed by Michael J. Vassallo upon interviewing Harry Douglas, Jr. after the younger Douglas contacted the author of this blog post: http://monomythic.wordpress.com/2009/08/17/marvel-mystery-monday-stuporman…
Probably Chesler Shop material, as Who's Who lists a "Harry Douglas" as possibly a member of that shop c. 1939-40, independent of its other theories about the "Harry / Douglas" signature.
Last appearance. Last appeared in Daring Mystery Comics (Marvel, 1940 series) #2. Strip was titled "Zephyr Jones and His Rocket-Ship".
Not enough is known about Schwartz to place the origin of this feature. Cal Cagno was on staff at Timely eventually, and possibly already at this point. He had been at Chesler in 1937 according to Jerry Bails' Who's Who, but this feature lacks the typical thick panel borders of Chesler work.
Probably in-house / freelance work.
Newt Alfred was at Chesler but this lacks the typical thick borders of Chesler Shop work (including other Alfred work for that shop). Erisman was from Goodman's pulp organization.
1X does the detecting for the team, 2X is a walking encyclopedia, and 3X is the strong arm.
Art spotting by Dr. Michael J. Vassallo. According to Edgar Loftin, both Bjorklund and Stalnaker worked more in pulps than comics, leading to speculation that this text piece may even have been bought for one of Goodman's pulp magazines originally.
Art credits suggested by Jerry Bails's Who's Who (listed under "Deep Sea Demon" rather than "Dave Dean").
Letterer credit by Craig Delich 2012-2-17.
First published by the Harry "A" Chesler-edited Ultem Publications, Inc., this was reprinted twice by Centaur after it bought out Ultem before being reprinted a third time here.
Chesler Shop material.
While the name "Dynamic Man" is strongly associated with Chesler, and the stories in issues #2 and #3 were produced by Chesler personnel, this story lacks the characteristic thick panel borders. Almost nothing is known about Daniel Peters, so his signature does not help place the source of the feature.
Probably *not* from the Chesler Shop, but the actual origin is unknown.