I've read this question about 20 times now and I guess I'm just not reading it with good will. This is the kind of thing that teachers would hit us with in logic classes. If you take the premise that "these four cards represent the rest of the deck" means that numbers with vowels are even and you confirm it by turning up just two cards and there is no other assignment of vowels to numbers even or oddness that can exist such that this rule isn't true. There are assignments of numbers and eveness that could hold for four cards such that cards with even numbers will have vowels but not hold true for the rest of the deck. It would in no way invalidate the premiss that "these four cards represent the rest of the deck" and still not make it true that all cards with even numbers have vowels on the other side.