Yesterday I did my covid extension in Chiang Mai and was stamped to Feb 28th. However I heard officers telling others who I *think* had under consideration stamps that if they renewed dec 15 it was 60 days from then and they were advised to come back closer to the end of the month (every person left unstamped) . So if you can get to the end of Feb now I would advise you to do so now. It will be a lot busier later in the month.
TLDR : Answer Summary
A user recently shared their experience of obtaining a COVID-19 visa extension in Chiang Mai, valid until February 28th. They noted that others received advice to return for renewal closer to the end of the month, as extensions could be granted for 60 days from a renewal date of December 15. The user recommends processing extensions now to avoid busier times later on.