I think the only thing that has to be done is that the credits be preserved. But the lack of an actual copyright has led to Night's unique situation (I believe).
The law was different when NOTLD was released. At that time, in order to get copyright protection, all works had to be released with a copyright notice (e.g., (C) 2004 Damin J. Toell). If there was no notice, the work was automatically put into the public domain. In the case of NOTLD, the title card bore the copyright notice, as was customary at that time. However, the title was changed before release, and the new title card mistakenly lacked the copyright notice. Thus, the film went into the public domain.
Over the last few decades, the law has changed. Now, one does not need to put a copyright notice on a work or even register the copyright. Copyright protection is now automatic.