If the coin hasn't been moved in 20 years, it's incredibly likely to have been 'lost' rather than saved. But again, in the very unlikely case that it's been 'saved', that's where the lost and found pool comes in. 'saved' keys can claim from the lost pool the amount of coins their entitled to.

If there aren't enough, then they'd have to wait until more coins enter that 'lost' pool.

The key wasn't lost, you've had it all along. But the system has assumed that you lost it since it hasn't moved in 20 years.