In that case, puzzling I agree! The only other thing I can think of is that IIRC it was for flights booked (paid) within the period not actually just travelled (which makes sense if you think about it as it's to refund you the dodgy paid surcharge) so maybe that's a big factor on your bookings?

Also (again IIRC), it's per return trip? Is that 20 returns or 10 returns?