i came in through BKK airport. But even before, in novembre, i came through Chiang Mai airport, and first, they required health certificate ... and had to argue, explain, before they let me in with a year long stamp.
from discussion with officer at immigration office in Chiang Mai: It is not a clear case to require/not require health insurance for older visa. Officer had to get permission from his boss, and his boss said no.
This is not for an extension. My 0-A visa was issue in Septembre 2019 (in Canada). I first entered Thailand in Septembre 2019 and had a stamp for one year. When entering Thailand in Decembre 2019, the 'new' requirement for health insurance came up, and had a stamp for one month only.
I have a Canadian passport. I applied and obtained a non-immigration visa in sept 2019 and I entered thailand with visa same month, sept 2019. I was stamped then with a one year stay.