You'd have to take it to the dealer to have them hook it up to DAS to determine the version. Or you insert the new disc and it will tell you your current version and ask if you want to update.Not trying to highjack your thread! But curious how do we find out which version is installed already?
If you have streets in your area that have been there a few years and are not showing up in your nav, then you likely have not been updated. If your car is say a 2009, then you are likely running a version from 2007 or 2008....depending on mfr date of your car.
There really isn't any risk in buying and inserting the disc. Once you've updated your maps (if they need it), you can re-sell the disc. $50 is a lot cheaper than taking it to the dealer to determine your current version or buying a disc from them for $250+.