Puzzled by Norton Antivirus 12 for Mac

I went to the NAV site to look at updates/upgrades and am puzzled by what it says about NAV 12. Seems to say the 2012 version only runs on Mac OS X v10.7. My Macbook is older and has Mac OS X v10.5.8. The Norton webpage says buying NAV 12 includes NAV 11 for people with the older Mac OS. Currently I have NAV Version 11.1.2 (17). Am I up-to-date, or do I need the NAV 12 version?