Sharing my experience getting a covid extension today (January 5) at Chang Watthana.
I was on a 30-day extension of my TR-60 visa. With that, I was good to stay until January 31. This is the first time I've been in Thailand.
When my number was called and I spoke with the officer, she saw that I was allowed to stay until January 31. She said I should come back later because I still have lots of time and the extension would start from today. I told her it's fine, I have a flight booked home in the first week of March, so 60 days from today is all I need. She was surprised but said all right and issued it to me.
Really, my original 30-day extension was mostly a waste of 1900 THB to get what worked out to be an extra 5 days or so, but I've been stressed out wondering if I'd be able to get the covid extension or not, so I applied for it earlier than planned. You need the 30-day TR extension before they'll give a covid one anyway. Applying for the covid extension so early would have allowed me to make other arrangements if I got rejected.
Things I had but no one looked at: a (refundable) flight booking on my phone, a printout of my TM30, a printout of the isolation requirements I'd be subject to if I flew back home, and an embassy letter.
Also, the officer that gives you a number required me to go downstairs and make a copy of my TM6 and copies of EVERY passport page. The print shop downstairs didn't make copies of every page; guess they knew that was BS. The copy of the TM6 wasn't needed either and I've still got it.