Mark, if you're just now getting your G4, and you've ordered from a reputable source such as BRD.com or RD.com, you can sleep easy, and know that it's definitely G4.
These sources ran out of G2 so long ago that it's virtually impossible for you to have been shipped "left over" G2.
But....
On the inside of the canister, G4 will include 3 (three) foam brushes, plus one fine-hair brush. G2 had only 2 foam brushes, plus the hair brush.
This determination method comes straight from the mouth of
VEIL Guy himself - and should be cross-verifiable either via old posts here or, alternatively, (where I know, for sure, such a statement exists) on the RadarDetector.net VEIL sub-Forum.
Hope this helps!