Above is the result of stacking images across 5 separate sessions. All taken by an unskilled beginner, so I am not surprised that the framing differs some across nights. The obvious answer is to remove sessions until I’m left with just ones where the framing is similar enough that the end result can be cropped without chopping off Central America
Presumably there is information in what would be the upper-right corner, but that is lost from the resulting fits image. I am curious if it is possible to control why/how Siril decides to rotate the images so that I could combine all 5 sessions.
If the solution is only to be more careful about framing in the first place - that’s an acceptable answer, too.