There's now a fresh page on Nintendo's support website, however, that seeks to clarify the reasons for level deletions. Filed under "A Course I Uploaded Seems to Have Disappeared. Where Did it Go?", it says the following, some of which is re-iterating known reasons.
Unfortunately, we sometimes have to delete courses from Course World. Below are cases where courses can be removed from the server:
- Low stars/plays
- After a fixed period of time, courses with low stars/plays will be automatically deleted from the server.
- Courses that include bugs that were unintended by either the course creator or the developers will be deleted. It's important that we remove levels with bugs quickly, because letting these levels remain in Course World can lead to negative outcomes for many players such as players experiencing levels in unfair ways that the original course creator did not intend, or re-writing "World Record" times.
- Requesting stars from other users
- Courses that are explicitly asking for stars from other players will be deleted. For example, users are unable to use words "Like", "Yeah!", and the "★" symbol in their course names. Please change the course name when saving a course that includes these words.
- Inappropriate Content
- Courses that contain something inappropriate, such as offensive language or phrases will be deleted.
- Other behavior in violation of the Nintendo Network Code of Conduct. Please note that repeated violations can result in additional penalties.
A number of these points may be challenged by some that feel stages have been removed unfairly. For example 'bugs' seems like a category open to challenge, as one of the joys in speedrunning is to find exploits and ways to effectively outwit the game itself. 'Inappropriate Content' and general code of conduct areas have perhaps been misused in past removals, too, such as when popular users like Grand_PooBear see their levels disappear. The key issue will also be whether Nintendo can more effectively communicate with users that see levels disappear, rather than just take them away and struggle to answer enquiries as to why.
In fairness to Nintendo, at least there's now some guidance in black and white. It may not appease the most dedicated members of the Super Mario Maker community, however, which means that these policies could still use some work.
Thanks to all that sent this in.