You could always have sites that only serve up indexes of NZB files (e.g. "NZB file => SHA-256"). Then you could use these to determine which NZB files to trust

You could always have sites that only serve up indexes of NZB files (e.g. "NZB file => SHA-256"). Then you could use these to determine which NZB files to trust. I would assume that distributing a "NZB => Checksum" hash would be a lot smaller/easier than running an entire site on top of a terabyte of NZB files.