I have NIS and it shows the version as 21.1.01.18.
If I run the Norton automatic update check from their web site it says this is the latest version.
If I run the update check manually from their web site it says this is the latest version.
I fooled the web site into thinking I had version 20 and downloaded the new version and installed it and now I have the LATEST version!
The moral is that you have to do a manual check and tell norton you have version 20.