I believe that if you refund now the funds will come out of your next upcoming payouts, then the day after the reservation was due to start you will receive the funds you are due, based on your cancellation policy.
That is how it is set up.
You could tell the guests that you will refund more money in future, but not until after you get the money. They can wait a year for the refund instead of you paying them now and waiting a year for the rebate.
Or maybe if you or the guest calls Airbnb they will do something different to help you out.
This issue arises when you offer a refund greater than your cancellation policy. If the refund goes through the normal Airbnb process and they refund according to your cancellation policy then there is no money collected from your future payouts and you get to keep whatever money comes to you when the reservation would have started.
Kerrin
City Limits Ranch