Ultimately, a DMCA notification is a notification that you have infringing content that can in principle be accessed / hosted through your sites. It's effectively a "friendly heads up" from the copyright owner that prevents you from being sued if you can take the content down expeditiously. It's a copyright owner saying "here are some URLs that could be infringing, and they need to be blocked." The author says "you don't know if the hash is already blocked in the web server configuration, or if the server is broken in some way that prevents access to that hash, etc", but that doesn't really matter—if they're already blocked, or inaccessible, then all you need to say is that that's so. Otherwise, it's on you to block them—it doesn't matter if anybody accessed them or not, just that they would be accessible if they're not blocked.