I have never been asked - including by JAL. I have one JAL award ticket US-TYO, then another BR ticket the following day to Taiwan. On the way back, I have a ticket into Japan, and another one from Japan back to the USA. No one has ever asked, not the airline, or immigration.

Next trip is coming up in November using the same format of tickets, so I will pay more attention if asked. One thing, I always check-in online, I never interact with airline staff until I am literally boarding the flight - maybe that has something to do with it.