The on-sale date is from the publication date recorded in the Catalog of Copyright Entries, Part 2, Periodicals, 1943, New Series, Vol. 38, No. 1.
Alter Ego #120 (September 2013) indicates that many panels of this story contained photostats of Captain Marvel Jr. figures adhered to the art pages.
Carlson is not credited on Hopalong by Jerry Bails' Who's Who, but he can be recognised by his horses. Very long, narrow tapering heads with two marked lines leading to the nostrils, and by the movement of the legs. Notice the outstretched frontlegs on page 2. Very special Carlson. Compare also with his Buck Jones stories, and the Rocky Lane stories by Carlson.