Umm.. I think it says what version it is on the box, which is slightly different for the two versions. I may be totally wrong, but I think the box design for 2.1 has the Mensa award stuff on it as opposed to the 2.0 box which does not. In either case, you're right that the decks are functionally the same, so either you have your box and you know or you don't have your box and it doesn't matter.
That probably doesn't help, but good luck anyway!