Apparently the "Unknown" issue in Ubuntu Software Center is not an issue and cannot be solved for the moment. From ubuntu lists, Feb'13 thread:
Your copyright file looks perfect. Unfortunately, software-center still doesn't actually parse the copyright file to gather that information. It seems to use "License: Open Source" or everything in Ubuntu main and universe, "Proprietary" for things in restricted, and "Unknown" for everything else. There is an open bug report about the issue here:
https://bugs.launchpad.net/ubuntu/+source/software-center/+bug/435183
They started working in the issue in July