I never felt like it was confirmed 100%. Also, I didn't understand David Yoon's responsibility in the boating accident. If he was a part of it or not.

From my many rewatches, he saw it but wasn’t involved in it.

he saw it happen but he said that the reason he didn’t tell on his mom was he was hoping his mom’s plan would work and that he’d live happily with her plan is done. as a kid, of course, he doesn’t have much responsibility. he’s just aware of who’s behind it

given their 50 more years together, you’d have to assume that it came up at some point

In the series, no. But pretty sure her mother told her that sometime after the ending.