Hey Lucas, I write AEUX. Selected shapes and text should export with no problem if they're on or off the artboard. Images, on the other hand, can only be exported if they are visible on the artboard. The workaround is to convert images to symbols with the button on the panel. It will create a sized artboard to export from so nothing gets cropped or ignored. This is a quirk with the way Sketch handles exporting.
Does that help? if not reach out at firstname.lastname@example.org.