How long do I have to report my stay on a Multi Entry Retirement Visa after entering Thailand?

Reporting is a separate issue to when your Visa expires and is only ever a 90 day sequence. The date will be in the paper attached to the last page in your passport.

I don't understand what you're asking referencing the 30 or 60 days.. when you entered you should have been stamped in for the duration of your year extension. And your entry stamp at the top should say Non-RE..

I am also doubtful you're here on any multiple entry Visa at all.

It is far more likely you're on a yearly extension of stay that you got from the immigration office and you also bought a multiple reentry permit.

Be that as it may if indeed you did enter on September 17th your 90-day report would be due 89 days after that date or on December 15th.

You can file a 90-day report in person from 2 weeks before the due date until one week after the due date. Soi in your case from Dec 1 until Dec 22.