With big enough numbers (and I assume there are a lot of these cards in circulation) it shouldn't be hard to make statistics and know exactly what percentage is never going to be claimed again.

That's the same tactic used by banks at a different scale, if everybody attempted to claim all the money in their accounts (during a bank run for instance) the whole thing would collapse, but they know it's not normally likely to happen so they keep only a fraction of the total savings available at any time.