From the word choice being used, sounds like the agent doesn't know what they're doing. It's not complex at all, the agent just needs to know what they're doing. Several FTers have booked on TG, even on Day 1 of *A.

Hold just the TPAC part, thank the agent, and hang up. Call back and get the rest done.

Also, in terms of your routing, I would recommend JFK-NRT on NH over EWR-NRT on CO if flying Business. Similarly JFK-UA-LAX-TG-BKK would be preferred to CO. JFK-LAX is UA Premium Serivce, and LAX-BKK is a serious haul.

Use the ANA tool to search for space and then request what you want. Then you'll know exactly what is available, and you will know based on the agent's responses whether they're with it or you need to hit that redial again.