The paid value of your voucher does not expire. If you have not redeemed your voucher by the expiration date, you can still use the paid value toward your purchase. Note that the paid value can only be used toward product cost, not shipping, taxes, or the purchase of another voucher or gift certificate.
For example, for a voucher worth $50 of photo books for $20, the paid value is $20 and the promotional value is $30. If you use it after it is expired, $20 will be deducted from your order total.