How does the Thai Revenue Department deal with income that is earned in a year when the taxpayer is not a tax resident, but which is remitted into Thailand in a year when the expatriate is a taxable resident?

Income from years when one is not a tax resident can be remitted into Thailand anytime in the future. Individuals are only liable for tax on assets that are remitted to Thailand when you are a tax resident. It is advised to keep very good records to prove this if asked in the future.