With the "lively discussion" on how the rule will be interpreted when you apply for the COE and when you stamp into the country, I will agree with
@Nongnuch *******
, there is no down side to applying for one of the insurance policies of the 18 listed companies to make sure you are covered to enter on your still valid visa sticker.
LMG with the 200K baht deductible policy is the cheapest (or was anyway)
Good luck with it. you clearly are ABLE to enter on the visa as it is still valid, BUT as far as if you can come in on your existing insurance (if it's not from one of the approved companies) OR if you will need to be insured by one of the aproved companies remains to be seen.