Here's what everyone always misses in any topic about Thai taxes:
When you fill out a tax return in your home country, you don't worry about tax treaty provisions, because all of your reported income is generated in your home county (for 99.9% of you).
Conversely, to fill out a Thai tax return, you will invoke provisions of a tax treaty (most of you) to reduce your tax liability. This is very different than your experience back home. And, it's unclear how much support for tax treaties are in the Thai tax forms.
Important note: those who work and pay taxes don't worry about tax treaties when filling out tax forms. What this means is 99+% of posters have no clue how to use tax treaties to reduce their Thai tax liability.
So this is going to be new to almost everybody.