It seems apparently that some categories of LTR Visa are entitled to an income tax exemption on foreign-sourced income (meaning 100% passive income from abroad) regardless of the year it is remitted in Thailand.
To be confirmed with BOI/Revenue Department.
https://www.belaws.com/thailand/ltr-visa-tax-benefits/
Income Tax Exemption
Wealthy Global Citizens, Wealthy Pensioners, and Work-from-Thailand Professionals eligible for the LTR Visa are entitled to an income tax exemption for income derived from a post or business conducted abroad or arising from assets located abroad that has been brought into Thailand.
It’s important to note that the tax concessions provided by the LTR Visa program are subject to rules and conditions prescribed by the Revenue Department.
Please note that this exemption does not apply to Highly Skilled Professional LTR holders.
https://sherrings.com/long-term-resident-visa-tax-concessions-thailand.html
For Wealthy Citizen, Retired and Work-from-Thailand foreigners who come and reside in Thailand under an LTR Visa:
A right to exemption from tax on income that's derived from a post or an office outside Thailand or business outside Thailand or property outside Thailand and brought into Thailand (i.e. an exemption from the Foreign Source Income Law)
To be confirmed with BOI/Revenue Department.
https://www.belaws.com/thailand/ltr-visa-tax-benefits/
Income Tax Exemption
Wealthy Global Citizens, Wealthy Pensioners, and Work-from-Thailand Professionals eligible for the LTR Visa are entitled to an income tax exemption for income derived from a post or business conducted abroad or arising from assets located abroad that has been brought into Thailand.
It’s important to note that the tax concessions provided by the LTR Visa program are subject to rules and conditions prescribed by the Revenue Department.
Please note that this exemption does not apply to Highly Skilled Professional LTR holders.
https://sherrings.com/long-term-resident-visa-tax-concessions-thailand.html
For Wealthy Citizen, Retired and Work-from-Thailand foreigners who come and reside in Thailand under an LTR Visa:
A right to exemption from tax on income that's derived from a post or an office outside Thailand or business outside Thailand or property outside Thailand and brought into Thailand (i.e. an exemption from the Foreign Source Income Law)