Originally Posted by
anabolism
I believe TAs can ticket on any airline that has the fare. Back when a number of people were buying xONEx tickets starting in origins for which most of the OW airlines had withdrawn their fares but a few hadn't yet, people were using TAs to get them ticketed on OW airlines that still had the fare, with the ticketing airline not being the first flight and maybe only having a small flight in the routing (I can't recall all the details).
A TA can issue it on GDS, yes. Whether QR will be unhappy with it (and as a result send debit memo to the agent or otherwise restrict the TA's future ability to sell QR tickets) is another issue. My experience in Taiwan is that TPEQR would only give okay to TA when the 1st inter-TC segment is on QR.