In May me and my wife flew MAN-BKK with QR and then BKK-CNX with TG on separate bookings.
For our return trip we went to check-in at Domestic Check-in for TG and they asked us if we had an onward international flight..... When we said yes we got sent round to International Check-in who checked us in for both the TG and QR flights. Our cases were checked-in all the way through to MAN and boarding passes issued for CNX-BKK, BKK-DOH and DOH-MAN.. We cleared Immigration at CNX and were given "CIQ" stickers and told to follow the "CIQ" signs at BKK.
Saved us a lot of time by not having to queue for check-in on QR at BKK..
Just booked another trip for October and again we have separate booking for QR and TG.