We married in SG, so had to show the KR22. I don't know why, they just needed some proof that I was still married the year before I guess, similarly to the 12 months bank statement.
Standard, KR2 or 22 paper from Amphoe. They even wanted this last year when I changed from O Marriage to O Retirement. The latter is highly recommended, easiest and fastest way possible if you have the finances.
The very first extension only counts as 90 days reporting date, so it should restart. From then on it runs independently from extension and only restarts should you leave and re-enter the country. But perhaps you had already some "under consideration" or other type of temporary extension. Or they just did not take it out. Play safe and do the reporting as stated on the last slip. In worst case they tell you to come back later. Otherwise you risk to pay 2000B penalty. Can all be done online in 10 mins.
90 days always runs independent. The only thing that resets it is your first extension of stay but this is entirely theoretical as they will still charge you 2000B penalty if you do not do it in time.