Does my 90-day reporting start 90 days after my non-O visa expiration date or my extension date?

strange they gave you that paper when you got the Non-O but if that's what they did that's when you go. Usually they put it in your passport when you get the yer extension

No problem, we've all been there.

The Non O is not valid anymore, it is replaced with your Extension of Stay. 90 Day reports don't have to match with the days you apply for Extension of Stay. For Example: if you travel abroad the day you enter Thailand again is the first day of a new 90 day period. There is a time frame within you can report, 15 days early to 7 days late, you applied for an Extension of Stay on 20 March it is not in this time frame. It means you have to visit again between 3 April and 23 April. If you have no travel plans next year, calculate the dates to get a match.

The date you have to report your address (90 day report) is set by this picture on 17 April 2018. You can do it 15 days before till 7 days late. That means you have to go back in that time frame to do your report.

Okay, normally when you get the Extension of Stay the also do the first report and you get a small paper stabled in your passport called Notification of Stay. In the upper left corner a small box with This is not an Extension of Stay, please report your address again on ../../..