If you are a tax resident in Thailand the tax return is submitted once per year by the 31st March following the tax year which is same as calendar year. Even of you are tax resident and have a TIN you may not need to submit a return of you have no assessable income. In fact some Tax Offices will not issue a TIN of you have no assessable income.
Anonymous participant I think they are currently having a bit of a tropical storm in the area. What about Ninh Binh about 3 hours by road from Hanoi? It on my list for maybe September but 100% in January.
I think it is similar with Brotish Embassy these days too. Saw a post this morning about a notary service for British Expats in Thailand who do the work for you and coordinate with Thai Embassy in UK. Maybe there is similar for US citizens?
Is your B still "Active" ie you left with a re-entry permit? Usually need to cancel existing visa before new one issued. Having said that there have been reports of people having DTV issued then cancelling the other visa upon return to Thailand. Usually have to cancel one though before getting another type. I did that for "O" to "B" but had to go through visa exempt between ie not valid visa when applying for B at embassy. As for your current business in Thailand are you closing it down? They might want to see you have nothing to do with it.
They might check attendance and further classes booked and paid for. It is not hard if they want to do it. Checking 500k will knock back plenty too if they went that route.