When does the 90-day reporting period start for a long-term visa in Thailand?

Did you check your passport; under the stapled blue-green receipt of paying for the extension to see if they put the small paper reminder of your first 90 day report? Many offices use that small paper.

The way it works is,

the 90 day count down starts from the date you applied for your yearly extension; meaning IF you got an under consideration stamp for your yearly extension it starts the day you received that stamp.

Your 90 day report is due 89 days from the date you applied for the yearly extension. So if Nov 15 was the date you APPLIED for the year extension your 90 day report is due Feb 12