That's a different situation then. :)
The agents won't upgrade until you enable the upgrade policies (Settings/All Settings/Agents/Plugins, or for Site Servers - Settings/All Settings/Notification Server/Site Server Settings: expand Task and Package Service folders and under Advanced you'll see the policies).
If you don't want to upgrade your agents, but still want communication between them and the upgraded NS, try enabling the Legacy Account Communication (Settings/All Settings/Notification Server/Notification Server Settings - Processing Tab).
Hope this helps!