If you credit CX*VN to Cathay Pacific, you would earn as if you are flying on CX.

During Check-in, VN will be able to add your DL number. However I have no idea whether miles would be credited (because it is under CX code, which it is usually CX who posts the miles)

Although, airline IT is not infallible

I don't know for the AA system that the OP uses. But BAEC is very good at catching flights OW-coded but operated by a non-OW airline.

I've had challenges re-scheduling segments via the website as well, despite clear availability in J and A via expertflyer. Has anyone recently had success with moving one or both dates of their tickets?

What are the dates you are seeing with availability in A? I'm having trouble just trying to price date changes on their website, which has been very clunky.

8/6-8/12 outbound from DAD-JFK, there is A each day on HKG-JFK, J on DAD-HKG, but crazy repricings on the website (fare class availability via expertflyer)

There have been multiple opinions and experiences voiced on this forum.
EF is useful as long as you use the proper POS/POO.
On EF we cannot see availability with VN POS.
I believe that it is A0 for the dates mentioned, as it is impossible to buy a fresh ticket in A fare bucket, only F is available at some USD30,000.

Thanks brunos. Is there a way to find VN POS short of just trying every date for ticket booking?

CX agents (both CX res and MPO) can tell you the VN POS figures if you ask on the phone. In my case it was A-3 from HK/US POS so even if my flight was F4A4, I had no luck changing my reservation for two under this fare (this being post first segment flown)

On the contrary, has anyone who booked the OPO mistake fares been able to change their date of travel? All CX agents I've spoken to say a reprice is necessary. For reference, my ticket is actually an OPO-SIN ticket but now the CX website doesn't show SIN as a valid destination anymore. A fare and J fare are available on the preferred dates.

I have another ticket confirmed on the date I would like to travel on as well as the origin as desired, but if possible, I definitely prefer the pricing of the OPO ticket

I don't understand your post. DO you mean that VN POS was A0?

Sorry, I essentially mean 'minus 3' from the max A availability.
So F4A4 for HK/US POS translated to A1 for VN POS. It is actually around half a day before my desired flight/time, EF showing F3A3 for HK/US POS but still no dice for my A class waitlist to clear, being on this VN fare.

This is a very interesting report. I am in a similar situation with needing to change an A fare ticket.

I just found some dates with Expert Flyer that were showing A5 J9 on DAD-JFK, JFK-DAD under both a US and HK POS. With those dates and flight numbers in hand, I went over to the CX Vietnam website and attempted to price out the itinerary. Unfortunately, no luck finding "standard" first fares only "flex" was listed for the flight numbers that were A5 on EF. Dates were July 14 and July 19.

Just for kicks, I also attempted to change my Expedia issued ticket online to those dates. That website only finds D/I-fare options and wants to charge me something like $623 ($525 fare diff + $100 change fee) for the privilege. No thanks.

So, it would appear that it isn't as simple as "A minus 3" for identifying VN POS inventory. May I ask what approximate dates you were considering? Perhaps the inventory difference is dependent on date/season...