Ok, with the situation with "that title key site", I have grown an interest in backing up the necessary files so I can use NUSGrabber or any other downloader without the site. I know that if I have some files I can do this, but I don't know exactly wich ones. And I don't want to (nor do I can or have the space to) backup most Wii U games on a hard drive, so it's much simpler to back something up for future download.
