Update-
Today I arrived in Bangkok via Suvarnabhmui. The IO asked about health insurance, I presented him my cellphone with a copy of the main English policy of health insurance from my country (not on the form they ask for!).
The IO read the policy for about 10 minutes, photographed the policy, my visa and passport, stamped in until 3/12/2020.
Notice- my health insurance is until mid March 2020. My visa O-A from 10/10/2019.
Good luck to everyone.
TLDR : Answer Summary
The user arrived in Bangkok with an O-A visa and was questioned about health insurance by the immigration officer. Despite showing an insurance policy that was not in the required format, the officer took time to review and accepted the document. The user's health insurance is valid until mid-March 2020, which is after their visa issuance date. Comments suggest that those with O-A visas issued before October 31, 2019, are not required to present health insurance.