THANKS A LOT for answering the questions. It helps a lot.

So Aeroplan offered to rebook the outbound (OZ) as well? If SQ on the inbound went missing, your BR most likely too. But OZ is still a mystery.

That is scary that Saudia site shows the itinerary fine yet something has gone wrong behind the scene. I was under the false security that as long as Saudia site pulls up the correct itinerary, the booking should be fine. Now your case demonstrates that things can still go wrong.

So now our only preventive action is to check partner airlines sites for the reservation, if it can be pulled up online. Or to call partner airlines to verify they see the things the same as we see.

Yes, they are Amadeus. You can check the bookings on SQ site with the Amadeus PNR, there is no need to call because you can select seats for J cabin months out.

I believe OZ can show partner booked itinerary from the memory when I used UA miles that incl OZ TATL ICN to FRA a few years ago.

I pulled up our reservation a few days after the booking in Mid Jan, for travel in Oct - all 3 Amadeus users (TP, SQ & BR) show the itinerary despite all of them have one TK segment missing, the one after the 1st stopover. BR also missing more segments before its flight but that is understandable.

Both SQ and BR allow seat selection online but SQ for some reason would not let me change the initial selection even though seats are available. SQ required you to provide an email address before proceeding, for the purpose of sending you a confirmation of your seat selection.

TP the "Additional Services" button does not work on our booking, not sure if it is because of redemption as people told me I can select seats in the Services area. I wound up used the online email form to contact them about how to do seat selection. Then I saw the seats assignment showed up a few days later, though not what I wanted. So I sent them another email to request specific seats. Should work just as before. They dont even have the seatmap for the brand new A330-900 neo - no where to be found on internet and I just guess with hunch - window side staggered.

At no time I ever think about calling any of these airlines, except TK due to it initially did not show the reservation on line. It took some time before TK system was updated with the AC booking and I can pull up reservation on TK site fine.
I want to see the actual reservation popped up on Partner sites after inputting the needed info. TK's a little weird - it wont take the ticket number initially but after it fails to do it with the PNR (not booked on its site directly) it would then have some internal redirection and then show up a screen specifically asked for the ticket numbers which it does recognize AC's 014 stock - then the itinerary shows up. Seat selection is available, albeit not intuitive, required some stumbling around even on the selection screen, but at the end it works.

You might be able to credit CX segment to some other FFP if it shows up internally still a revenue ticket. AS would be my choice.