This is correct. You have to deal with the TA/issuer until the day of departure for the outbound (or eventually the day before when OLCI starts). You can deal with the carrier directly on the day of departure to handle change of flights, stand-by, paid upgades, etc (note that paid upgrades can be handled directly with the airline as soon as OLCI opens). Then once the outbound is flown, you can also usually deal directly with the carrier to handle changes for the return flight.