Changing to a cheaper flight, and then a more expensive one
My parents were planning to fly from Dublin to the US on Aer Lingus in business on Saturday - unfortunately my Dad was in Amsterdam last weekend, so won't be allowed into the US. We can change the flights without fee, but right now all flights in the future are cheaper than the present booking is worth. I understand that if they change to a cheaper flight then they won't be refunded the difference, but if they change to (say) a flight in August now, will any record of the original fare be kept if they then end up wanting to (say) change to a more expensive flight in July - ie, if they paid X last month, switch to a flight that's 0.8X now and then change again to a flight that's 0.9X would that still be free or would they need to pay the fare difference between 0.8X and 0.9X?
(After 90 minutes on hold earlier today, the official line appears to be that if a passenger is suddenly no longer going to be allowed into the US, that's the passenger's problem…)