1. Wouldn't I have the same problem trying to explain to Immigration that I got a new visa while still on extension as I would talking to an IO at airport arrivals? (I didn't want to cancel my old extension until I had confirmation that I was approved for the DTV since I've heard so many stories of people being denied.) If it matters, my extension was granted at Chiang Mai.
2, Even if I missed it and they stamped me in on my old extension, wouldn't my DTV still be valid for my next entry since it's multiple entry? As it happens, I expect to be out of the country when my extension expires.
The 800k baht? That's one of the reasons I wanted to switch to the DTV. It frees up 1.6 mil baht for me and my wife. We both fulfilled the obligation to keep 800k in the bank for over 6 months.
I think "prosecuted" is the wrong question. Has anyone on a DTV, TV, or retirement extension on an O or O-A visa, or anyone who does not have a work permit ever been "asked" for a tax return?
I have a Thai TIN but the last time I filed a thai tax return was 2008 and I've spent over 180 days a year here every year since. I'm still waiting for someone official to ask for my tax return.