As @DalindaBohr , explained, the solution is to always "import" content into the target course shell and then "remove the dates." Always start from the target course, and bring items into it with "import.' When doing so, one should always import "selected content."
The issue with Canvas is that too many instructors try to "copy" content from the old course shell into the target course. The old dates are carried over. Because so many instructors get hung up, the Canvas developers should address this problem.
Lastly, a lot of instructors erroneously believe that they have to move everything into Commons as an intermediary step. Unless they want to share their content with others, there's no need to do this. Instead, a development course, commonly referred to as a Sandbox course, is a better way to store course materials long term.
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