Quick, name a DC series that started out in Mystery in Space, then continued in Strange Adventures in the 1960s.
Did you say Adam Strange? Wrong! Adam Strange did start out in Mystery in Space, but the Strange Adventures stories were all reprints with the exception of #222, which featured a new Adam Strange story, but which was dated Jan-Feb 1970.
The answer, and it's a tough one, is Star Rovers. The Star Rovers were a trio of space explorers and adventurers. Glamorous Karel Sorenson was a former Miss Solar System and expert shot, while playboy Rick Purvis was a big game hunter. The final member was novelist and sportsman Homer Glint.
The series seems in some ways the Atomic Knights equivalent in Mystery In Space, in that they did not appear in every issue, but every few issues. However, unlike Atomic Knights, Star Rovers was more traditional in some ways and yet more offbeat. It was traditional in that the stories were formulaic. The Star Rovers would be asked to solve some mystery and each would come to a conclusion that debunked the others, and yet in the end all three would be proven wrong.
Indeed, within a few stories they were all remarking on that fact:
The titles to the stories were all questions:
MIS #66: Who Shot the Loborilla?
MIS #69: What Happened on Sirius-4?
MIS #74: Where Is The Paradise of Space?
MIS #77: Where Was I Born? Venus? Mars? Jupiter?
MIS #80: Who Saved the Earth?
MIS #83: Who Went Where? and Why?
MIS #86: When Did Earth Vanish?
At this point, though, Julius Schwartz, the editor of MIS ran into a problem that was actually fairly common at DC over the years: he inherited a new feature. Hawkman, who had been having trouble earning his own title despite a pair of three-issue tryouts in Brave and Bold was assigned to Mystery in Space, which left no room for the Rovers. So they scurried over to Strange Adventures #159 and #163 before finally being retired. They never made the cover of any magazine they appeared in; they were strictly backup material.
And yet there is a certain charm to the series. Gardner Fox tinkered with the formula a bit, and so the Rovers were not always wrong despite frequent initial misconceptions. Sid Greene's artwork was perfect for the slightly humorous sci-fi settings. And it cut against the grain of DC's typical heroes who always figured out the most cryptic mysteries on their own.
Correction: I originally said Sid Broome. My bad!