The second half is just wrong. There's no such thing as unused balance on an iTunes card. When you redeem a card, the entire balance is credited to your account

The second half is just wrong. There's no such thing as unused balance on an iTunes card. When you redeem a card, the entire balance is credited to your account. The credit will only go unused if you stop using the iTunes store, so that's at most $1.28 per user, not per card.