A usenet download can either fail due to being taken down after a DMCA or similar request, not being in one of the newsgroups cached by one’s usenet provider, or because one’s usenet provider has fewer days of retention than the age of the usenet release. In terms of telling a binary newsreader program (i.e. downloader) such as SABnzbd or NZBGet what your provider is, there’s a page in the settings of those and similar applications to enter the domain name, port, username, and password associated with any usenet provider subscriptions and/or block plans you have.