Separate flight ticket purchased, am I still eligible for free transit?

Hi,

I am a Korean, living in America and my family is currently living in Ningbo, China. I was spending my summer with them in Ningbo on a L type, but I am planning to spend my vacation in Thailand in 2 weeks. Irrelevant to the Thailand trip, I have booked my plane ticket from Shanghai to LA in advance. Since the meantime of both trip is only 3 days, I was wondering if I am still applicable for free transit when I have purchased both trips completely separately. Like would Bangkok airport let me fly to Shanghai without a valid visa?

I have booked the round trip from Shanghai to Bangkok. That being said, I will come back to Shanghai after my vacation and then 3 days later, I am flying from Shanghai to LA.
Thanks,
Angela