i had a non o-a visa, issue in Sept. 2019. I arrived in Thailand in Septembre. Later, i traveled/returned in Oct and had first issue that an insurance certificate was required. I mentioned that it didn't not apply to Pre-October 2019 and they let me in (after a long conversation). This time, i just landed in Bangkok, and they said, that without insurance certificate, no matter when i got my non o-a visa, i can only get a one month stay. They told me to To stay longer (i plan to stay 2 months before traveling again), i have to get an extension from CM immigration office. Thank you for you advices !