Not sure if the backend process here has changed, but I had a really easy experience at IAD with an IAD-SFO Y ticket and SFO-MNL J ticket.

1. Kiosk spit out a tag to SFO (as expected)
2. went to agent behind computer. She needed confirmation number, fare class, and flight number for the subsequent leg.
3. No more than 15 seconds after having that information a new tag came out.

I was able to track the bag through UA app bag tracking system. It was a little broken in that reported the bag would not make the SFO transfer, but did show each scan in turn as it went through.

it took more work to get into the IAD Polaris lounge than it did getting the bag tag printed.