I have a 12-month ongoing retirement extension and also have a yearly AETNA insurance plan that covers Covid and is good for re-entry into Thailand. I have read that the Covid insurance coverage should cover the length of your visa. How can this work with yearly renewable plans if the retirement extension and insurance policy do not start on exactly the same date? I plan to leave Thailand for 3 months soon and on my return in January my yearly insurance expiry date is before my retirement extension needs renewing. Anybody had this issue when applying for a CoE? If so was the CoE application accepted?

Dor ceo you can get 1 month or more months of covid cover, from 1500 tp 2500b per month. You can chose date just as your health onsurance expires. 
But till january there might be no coe anymore and your existing health insurance might be sufficient. 
things go now in the good direction. I would not worry, if coe is refused you got 2 weeks to buy covid insurance. Some consulates become already liberal to stict red tape