Hi @CHARLESDEAN ...
Cross-listing two or more courses together moves all enrollments from one course to another. For example, if you had three courses (A, B, and C), and you wanted to cross-list all of these courses together so that all enrollments from courses B and C flow into course A, you can do that. Cross-listing does not move course content...only enrollments. In this example, course A will be the only course that you and your students would see on your/their Canvas Dashboard. Even though students registered for courses B and C, they will log into course A within Canvas. You should be able to publish course A, and all students from all three courses would be able to access the content...provided that your course start date and access settings are correct within your course "Settings" screen. You wouldn't need to publish courses B and C because you and your students wouldn't see those courses. If you log into course A and look at your "People" page, you should see all students listed from courses A, B, and C.
Yes, there is a way to de-cross-list courses so that these three courses in my example would return to normal...i.e. three separate course shells. But, you shouldn't need to do that just to make sure your courses are published.
I hope this helps to clarify things about cross-listing. Let Community members know if you have any other questions about this...thanks!