This is far from a ‘solid’ data point to the contrary. A TA/ someone experienced in ticketing might know better.

Slow as I am, took me a while to figure that there wasn’t any harm in trying. Called CX, but, D availability was gone by that point. The agent added a waitlist (same flight that we were in B class on).

While trying to check-in for the original booking, got an e-ticket error & realised that the waitlist had cleared. Called in and the agent created a ‘case’ to send to the rtw team on priority and told me that they would call me the same day to confirm on things. While I was reachable, I asked for a comment to be added to just get the change (B->D) done, in case there wasn’t any difference to be collected.

An hour later, got an updated itinerary, with the B booking for the 1st segment dropped. Still noted the same e-ticketed numbers as earlier & couldn’t check in still.

Some half an hour later, got new e-tickets. They note “NO ADC”.

While it (no re-faring higher) might be all within the rules, I am surprised. I’ve had a tax recalculation done in such cases in the past & the JPY has moved a fair bit since we booked. CTS-HKG is a tricky sector for CX this time of the year- 4pax on the booking- CX DM/GO/2xSL (OWE/S/R). Wife did have a separate outstanding issue with CX (bag missed connection to CTS, wrong info given on arrival causing a day without winter gear in a remote resort). I have seen CX ‘make up’ via other/unrelated means- but that would typically be something like clearing the D waitlist- not, ticketing.