My understanding is that the sale discussed in this thread has not closed yet. What sellers need to do is see if and how the refund will be treated at closing, I.e., are the closing documents saying anything about it. Also, what are they saying about payment of 2021 dues.
The closings should require that any dues still owed to DVC for the year will be paid in full to DVC as part of the closing. The sellers need to be aware that those dues that must be paid at closing are now all the 2021 dues. They also need to be aware that they are still the owners that are liable for all those dues if closing has not yet occurred.
Typically, when closings are this early in the year, the buyer will likely be paying those dues as part of closing unless the parties have agreed otherwise. But, in that case, what is actually occurring is that buyer would be paying the liability for 2021 dues that the seller actually owes. Thus, if the seller is going to raise the issue that he should get the refund, the easy response from the buyer Is that the seller, who currently owes all the 2021 dues has already gotten credit for that refund from DVC; the buyers only liability should be for 2021 dues still owed after that refund. One could perhaps try to negotiate otherwise.
The issue is thus not one that depends on seeking a refund from DVC, which when it issued the lower dues bill for 2021, had already applied the refund to the seller’s liability for those dues. It is instead just an issue between the seller and the buyer.