If usual trips are between Sep and Nov, then your ideal use year is likely August, although June would also be fine (there Is no July use year). Why August:
1. Use year does not determine when you can go, which is any time of year, or when you can first go online or call to make a reservation, which is always 11-months from date of arrival at your home resort and 7-months at other
DVC Resorts.
2. A key reason to choose a use year that begins shortly before you usually go annually simply has to do with the risk of cancellation of a reservation. As long as you cancel a reservation 31 or more days before arrival, any points used go back into your account in the same status they had when put into the reservation -- current use year points go back into the current use year, banked or borrowed use year points stay in the use year into which they were banked or borrowed. If you cancel a reservation 30 days or fewer out, all points go into holding (which has been temporarily suspended during this Covid time), something you definitely want to avoid because points in holding all expire at the end of the existing use year and can be used only to make reservations 60 days or fewer from arrival date, which for DVC can often be something that is impossible to do because rooms will fill before 60 days out.
3. But cancelling 31 days or more out can itself be a disaster if it is a reservation that was set up to take place near the end of your use year. Example: assume an August use year and you make a reservation for July 2021 in Aug 2020, and you have to cancel reservation at the end of May 2021 more than 30-days from date of arrival. If there are any banked Aug 2019 points or borrowed Aug 2021 points that are returned from that reservation, they must be used for a trip that ends by no later than July 31, 2021. The same applies to any current August 2020 use year points that return to your account because you only have until the end of the eighth month of your use year, March 31 for an August use year, to bank all your points. In other words, if you cancel at end of May, you would have only about 60 days left to make another reservation that uses any of those points, which again is something often impossible to do.
4. Now assume you have an August use year and make a reservation in Oct 2020 for September 2021, using "current" use year points from the Aug 2021 use year, and banked Aug 2020 use year points, and borrowed points from the Aug 2022 use year. And then you find at end of July 2021 that you have to cancel. All those points go back into the Aug 2021 use year and you have until July 31, 2022 to use them, and can even even bank the Aug 2021 points into the August 2022 use year. Result: no real risk of losing the points due to the cancellation. That is the main benefit for having a use year that begins shortly before you usually go to WDW.
5. Why August (or June which would accomplish the same thing) rather than a September use year. For many, September would likely be fine in that situation. But, particularly because Sep now has a stretch of days that have the lowest point requirements of the year, you have a second factor to consider and it is called "walking a reservation." A large proportion of DVC Members are naturally bargain-oriented (e.g., a main reason to buy DVC is to avoid paying very high hotel room costs for every stay), and desire to get rooms that have the least nightly point cost at the resort they own, particularly during lower point cost seasons, but the number of available rooms in that low-point-cost category are too few to meet the demand. What now exists is a problem of getting a number of rooms even at 11-months out, e.g., at times they go full at nanoseconds after the ability to reserve opens at 8 a.m. at 11-months out; the winners are simply those whose computers communicate fastest with Disney's computers. With varying degrees of the problem, those rooms include AKV value studios, BLT standard studios, BWV standard and boardwalk view studios, VGF studios, and CCV studios.
6. If your desire is to get any room that has an 11-month reservation issue, and you want to go in September, then an August use year will be better than September. That is because you can start "walking a reservation" with August arrival dates, which you cannot do with a September use year. Walking consists of actually doing a reservation before the time you want and then modifying it regularly until you have the dates you want. For example, suppose you want Sep 10-17, 2021. As is often the case, a number of those rooms with an 11-month issue may actually be open at 11-months out for much of Aug, although they may be near impossible to get at 11-months out for a September start date. So what happens is that at 11-months out you find a day in Aug 2021 to make a 7-night reservation. Then every 6-days or less, you modify that reservation to a new 7-day period without having to cancel the existing reservation first. Continue that process until you have the actual dates in Sep that you want. Why does that work? Once you make a reservation 11-months, the room you have cannot be reserved by anyone else at 11-months out from any night you actually have the room reserved. For example, if you have Aug 10-17 2021, no one else trying to book at exactly 11-months out for start dates from Aug 10 to Aug 16 can get your room for such a start date or any nights thereafter. As long as you continuously modify the resorvation at least every 6 days, you will end up with the Sep dates you actually want.
7. The problem with a Sep use year in that situation is that the earliest you can begin a walk is for an arrival date that is on or after the beginning of the use year in which your trip will take place, e.g., in that case an Aug 2021 reservation would need for you to borrow Sep 2021 points to make it and once borrowed they cannot be put back into the Sep 2021 use year and thus cannot be used to "walk" to a Sep 2021 trip. Thus, for that Sep reservation, you could not start a "walking" reservation in Aug. As a result, if your desire is to get one of those difficult to reserve rooms and start a walk for a Sep (or even Oct) reservation in August, you need an August use year not September.