Dec. 2020 UY starts on Dec. 1st, 2020 and expires on Nov. 30th, 2021.
Booking date is not related to date of travel. You can book even if it's not Dec. 1st, 2020 yet (meaning you don't get your Dec. 2020 UY point yet), so long as the reservation / date of travel starts after Dec. 1st, 2020. If the date of travel were to be on Nov. 30th, 2020 or earlier, than you will be borrowing from your Dec. 2020 UY, since any reservations before Nov. 30th, 2020 is technically in your Dec. 2019 UY. You must borrow 2020 UY points if you want to make a reservations for dates that fall into your 2019 UY, if you don't have any 2019 UY points left. For reservations for Dec. 1st, 2020 and afterwards, you are not borrowing points, you are just using points from your regular Dec. 2020 UY allotment.
So, yes, you can book at the 11 month window for Feb, 28th 2021 at your home resort today, which will fall in your Dec. 2020 UY. If you want to book for say March, 15th, 2021, than you must wait until April 15th, 2020 before you can book that start date.
This assumes your contract is already closed, and transferred into your name by
DVC Member Administration. If you haven't closed yet, you can't do anything, and must wait.
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