Follow CarolMN's advice above. Particularly for December reservations, which is the highest
DVC demand month of the year at WDW (the highest demand weeks of the year are first and second week of Dec, and Christmas week), the safest course is to book 11-months out to avoid being disappointed, particularly if home resort is an MK or Epcot area resort.
Thus, if you need those Aug 2022 points to reserve your desired Dec trip, you should be banking them now, or no later than the day before your 11-month window begins in Jan 2023. If you want to hold back on banking the Aug 2022 points now because you may also attempt another trip that ends before July 31, 2023, and you have enough Aug 2023 points to make the desired Dec reservation, you could do the reservation in Jan 2023 without using banked Aug 2022 points, and then, as long as you bank the points by March 31, 2023, you could, right after banking, "modify" your Dec reservation online to the same resort, room category, and dates that you already have for that Dec 2023 trip, and, as long as the banked points are part of the contracts you list for the modification when doing it, the system will use banked points first for the modified reservation and take out the same number of Aug 2023 points that you had in the Dec 2023 reservation.
And, as noted, any banked points remain in the use year into which you have banked them, and must be used for a reservation during that use year before it ends, i.e., they cannot be banked again to a subsequent use year or brought back for use in the their original use year.
