So we're flying SYD-AKL_EZE in November this year. The SYD-AKL legs are AirNZ, AKL-EZE legs by China Eastern. Booking made by a TA - first time we've used one in donkey's years.
What we have discovered is that, because the tickets were issued by a TA, we are not able to access our booking on China Eastern's website or app, despite having a PNR. This is apparently because China Eastern 1) don't use PNRs at the moment (they've taken customer feedback and will maybe consider it sometime soon) and 2) unless the ticket is purchased
directly from the airline, you can't use the website or app to Manage your Booking, anyway.
Not using a PNR, such access requires three factors: ticket number, name, and ID Document number. So thinking it might be a passport number issue I went to China Eastern's Sydney office. They verified my booking and ticket was all in order, but there's no passport details attached to our booking and anyway, they couldn't add them as the tickets were TA issued (which TAs can do without supplying traveller ID, even though we had provided that), and those details would be captured at the checkin desk on the day. Regardless, wouldn't have mattered, as only tickets purchased directly from the airline can be used to access their website and app!
The TA indicated that there was nothing more they could do, either.
So the bottom line is that the only the TA can manage our flights due to how the tickets are issued. It also affects our managing the AirNZ flights, even though it has it's own PNR because it was all done through China Eastern. If there are any issues, the airline's system will notify the TA, and hopefully the TA can reach us.
Something to be aware of, which we weren't at the time, having been independent travelers for decades.