A more thorough explanation:

The Single-Registration Rule is a doctrine followed by the U.S. Copyright Office that allows only one registration for each original work. This means that once a work has been registered, it cannot be registered again.

For example, if a musician registers a song with the Copyright Office, they cannot register the same song again under a different title or with minor changes to the lyrics or melody.

However, there are exceptions to this rule. If an unpublished work is later published, the creator can register it again. Additionally, if a work has been substantially revised, the creator may be allowed to file a supplemental registration.

For instance, if an author revises a book and the changes are significant enough to be considered a new edition, they can register the revised edition separately from the original edition.

The Single-Registration Rule is important because it helps to prevent copyright infringement and ensures that creators receive proper credit and compensation for their work.