The flight plan for the aircraft, Sydney to Hong Kong, was received at Brisbane Air Traffic Control at approximately 1130 hours EST with a planned departure time from Sydney of 1300 hours. A departure message was received at 1325 hours. No other flight plan details were received on the aircraft by either Brisbane or Darwin Air Traffic Control. At 1540 hours, the aircraft reported at Mt Isa, estimating position BROCK at 1600 hours. According to the flight plan, the next position reporting point should have been GOVE. There was no conflicting traffic and the aircraft was cleared via BROCK. Twenty minutes prior to the aircraft's departure from Sydney, the aircraft commander was advised of an increase in zero fuel weight for the aircraft and amended the flight plan as a result. The handling agent for the operator failed to submit the updated plan. The reason for this omission was not determined.