There are a few other stories from this period that I've spent days considering and finally decided to leave off the list, and it's the inking that's made it hard to tell.
For what it's worth, in every story below, the final panel closes as you see in "Horror Island"—with "End", rather than "The End" as in the other features in these issues.
Paul Cooper pencils on Sub-Mariner
in Marvel Mystery Comics
|Sep/45||66||Sub-Mariner vs. the Murderous "Zako"|
|Nov/||67||The Lost Soldier|
in Human Torch
|Fall/45||20||The Carnival Murders|
|Win/46||21||Murder in Blackout|
in All Winners
|Sum/45||16||The Fabulous Racket|
in All Select