Thinking about this again per your response, I would agree that the kg limit for luggage is part of the promised service (either specified on the ticket / invoice to you or part of the allowances published on an airline’s page at time of purchase of ticket and confirmed in an airline’s T&Cs), but specifically on seats / layout, I have never seen any promise on a ticket as to airplane type / seating / pitch?

Well, look like it worked out in your favour after your following up with MH, again, I am glad to learn otherwise, but I was under the impression the ticket only guaranteed the transport from A->B, in-line with the T&Cs of the tickets themselves (which should be aligned with relevant regs).

​I have had the same be done to me on SQ (or was it 9W?) for a trip between India and Singapore a number of years ago, and had thought the best one could hope for was a few thousand miles in such cases as an appeasement. If there’s industry practice to the contrary, I am definitely interested to have that as a point of reference for similar issues in the future.