I emailed member services and received this response....
Dear Kristen,
Thank you for contacting the Walt Disney World® Resort. Thank you so much for joining the Annual Passholder family!
I did a lot of research for the answer and even called the ticket services. Since this is a brand new annual pass you can activate the new Gold pass any time between now and December of 2030 and you will get the 13 month promotion Gold pass that you paid for. So yes you can activate the Gold Annual pass certificate in fall of 2018 and get the full 13 months that you paid for.
We hope this information helps with the planning of all the upcoming magical vacations!
If you have questions or need further assistance, feel free to contact us.
Sincerely,
Janelle Gillette
eCommerce Sales and Service Team
EDIT: (I was typing the previous response from my phone so let me elaborate...)
This is the message that I sent to Member Services...
"I purchased a DVC Gold AP during the 13-month promotion. I received the "green card voucher" in the mail and I have the AP linked to my My Disney Experience account. I was planning to use it for my trip this fall, but plans have changed and I do not want to activate it until the fall of 2018. When I do that, will it still be good for 13 months? I have the opportunity to use the military ticket in 2017 because my travel companion is a member of the armed forces. I have a 6-day trip planned in 10/18 and another 8-day trip planned in 10/19, but those trips will not fall within 12 months of each other which is why I need to know if the AP will still hold it's 13-month "value" if I wait until October 2018 to activate it. Can you provide me with a definitive answer? I saw on different message boards that the AP must be activated by the end of 2017 in order to retain the 13-month expiration. Otherwise, it reverts back to a standard 12-month pass. I really need this information because if I don't plan this correctly, it will cost me a LOT of money. Thanks!"