Knowing the way software works, this is my guess: If you did not get a “XXXX has cancelled because of COVID” email for a cancelled guest, or if you did not say “yes” when getting the “XXXX is uncomfortable traveling and wants a full refund” email, then that booking will not qualify under the 12.5% refund policy.
I granted a few full refunds manually before the 100% refund policy went into effect, and there is proof through messaging that the cancellation was due to COVID, but I doubt those bookings will be included in the 12.5% refund policy. In order to get 12.5% back from those bookings, calling Airbnb and pointing them to the messaging to prove that the reason for cancellation was COVID might help, but obviously that’s hit or miss at best.
I don’t think this refund policy can work any other way, as Airbnb would have to spend 1000’s of hours combing through messages to determine the reason for each cancellation.
Similarly and for these reasons, I doubt that Airbnb will take the time to include your “retroactive” bookings for the 12.5% refund policy, at least not automatically. Therefore, you will probably get your 50% payout for those bookings.