Even the definition of the very word "ticket" is perhaps not as clear-cut as it might seem.

We all know that nowadays we are effectively issued by the carrier with an itinerary and/or e-ticket, call it what you will. It can be printed out, although interestingly enough there are many occasions when it makes no difference at all if you show up at an airport without it because your booking will simply be traced from your passport (as I experienced myself a few days ago at DXB).

In times past, physical paper tickets were an absolute essential (as illustrated by the fact that losing one would create all manner of complications!). However .......for multi-sector bookings, there would be a separate tear-off coupon covering each sector. Some might consider these coupons as individual tickets in their own right ; which case it would - in today's world - be a matter of isolating the downgraded sector by basing any refund on the coupon or "ticket" applicable to that sector.

Just a thought .......