Often on the US-Asia flights, especially the ones that have continuation flights from NRT (are there any flight nos. that terminate at NRT?), the flight will be referred to on channel 9 with the flight no+letter, as long as the same flight number is still in the air somewhere.

On one ORD-NRT run I was on, the pilot announced this with the same explanation before take off, so passengers listening wouldn't be alarmed.