As you can read before my current understanding is as I posted before seeing US retirement accounts as very different than regular bank savings or regular outside retirement account investments. To add for regular outside retirement account investments I think the Thai rules are clear. It's irrelevant what you held before 2024. The accounting is done based on a profit cost basis, if any, if remitted as a Thai tax resident. But if you made that move before 2024 and banked it then that cash would be excluded.
I don't think we're going to know anything totally definitive on this issue for a long time and even then it may be office by office.
Reports of audit results where someone is challenged for not doing it the way I posted would be great precedent, but who knows when or if such reports will come forward.
On the other hand, doing it the way I currently understand as correct would create the maximum tax liability of any interpretation, so there would be zero reason for that to be audited. As the Integrity Legal guy says -- no taxing authority is in the business of helping people pay LESS tax.