Originally Posted by WineCountryUA

Generally for UA to issue a ticket it needs to have at least one UA operated segment. or a UA labeled codeshare or be joint venture flight or ....
UA has been getting more strict about this in recent years

Additionally the operating airline needs to allow the flight / fare to be plated on a UA ticket stock.

So it is unlikely UA will ticket an ANA only itin for TYO-SIN (unless it is offered as a UA codeshare which I don't see)