All EMDs issued as a voucher from an partially/wholly unused ticket had their validity periods extended from 1 year to 2 years from its date of issuance (not the date of the original flight nor the date of the ticket issue date).

Those who didn't have the additional 10% were also reissued, with a 10% additional non-refundable value added.

Edit: I would agree with ISTFlyer that you should check the expiry date. When calling, ask to check the expiry date of your EMD, DO NOT call it a voucher as some agents will get confused (I've had one tell me vouchers don't exist).