I flew the original date I booked. However, if you were to change your first segment I believe the ticket validity would still be one year from the date of your original first segment.

really impressed with CX. booked DAD-HKG-JFK and a separate Avios Y ticket on JFK-YVR for the same day. CX in DAD "found" my other ticket without needing me to show anything, checked me all the way through, moved my Y seat at the back of the bus to a bulkhead seat and even gave me F lounge access in JFK!! looks like this trip is off to a good start

Does anyone know the answer to the below question?

I had booked 5 of these deals. Had to cancel 4 of them as I couldn't go! how annoying

cx ground staff in jfk
 

Did anyone flying return from JFK have ground staff check for a outbound ticket from Vietnam (on separate ticket to make sure you leave country within max days allowed on visa)? Didn't purchase one as I was planning on skipping the last leg from HKG to DAD, now wondering if I should have a refundable one just in case or tell them that I'll purchase one once landing in Vietnam.

Yes. They are supposed to check, if they don't they're not doing their job.

I flew my one and only ticket last week, and they did check at JFK - both my Vietnam visa and subsequent flight to leave Da Nang. That was the main reason why I decided not to throw away the last leg and book a different flight home from HKG - I didn't want to have to book a fully refundable ticket from Vietnam to satisfy this requirement. Of course, they might have let me board if I had explained that I was not planning on taking the last flight, but not a risk I wanted to take.

This is a huge thread, but IIRC somewhere upthread (or possibly a different thread?) someone was denied boarding in the US for not having it in place.

This corroborates what I've read upthread overall, that CX seems to be playing the mistake fare flyers by the book. They bit the bullet and aren't handing out extra favors.

For me, not this fare but J Vietnam-HKG-USA last year. Not JFK but LAX. The ground staff requested me to show her the ticket from Vietnam back to HK (I'm a HK resident). I've got one refundable by another airline based on previous experience and scrapped through! At the boarding gate, the staff again requested for the ticket, and they had to type that flight number into the system.

And quite right too.

I don't think that this is specific to the VN mistake fare.
Airlines do carefully check that you meet VN immigration requirements when boarding overseas.

I believe that arguing that you are not going to use the last leg HKG-VN is not going to do the job.

are the fares fully refundable or did you have to pay a cancellation charge?