You must have good reasons to do this (maybe some business in SIN or a mileage run). Otherwise, I would advise you to fly IAD-NRT on UA and then go direct to ICN with a two hours flight as opposed to the 2 days routing you are taking. it would be much preferable to fly NRT-ICN nonstop in Y for 2 hours than what you are doing, even in J. You seem to privilege *A but both NH & OZ have numerous daily flights, even UA. So there will be plenty of award seats in Y and even the cost of a paid ticket is small.