Actually all of them are numbered like that I believe. It's confusing because it represents the card number in the set rather than actually being numbered (someone do correct me If I'm wrong).
Another example would be 11-12 Elite. Every card on the back of the "stars" said X of X.
That's not a serial number. It the card number in the set of 36 cards.
Thanks, I just come back from due digital and you're right.