You can look in the Command Center and see if it shows up as installed and up to date. Or within Sonar you can add an effect to any track and see if it exists as an option to install.
I have had a similar question to the O.P.'s all along - a good example is Addictive Drums. When I purchase an outside plug-in, and then it gets added as a freebie within Sonar, how do I know when Sonar has a "light" version so that I don't install / update a light version over my better, purchased version, versus Sonar's freebie being the full Monty? With AD I have the full package, latest, so I have never allowed the Command Center to "upgrade" the Sonar version for fear I'll overwrite my full package. But what about other plug-ins that are similarly available from vendors (I think some Softube applications fall in this category) - how do we know what's a full version that should be upgraded, and what's a "light" version?