What Are the Requirements for Extending an OA Visa Stay in Thailand?

Kind thanks for your guidance. I want to verify that I will meet the requirements for an extension of stay over 50 since there is little chance that I can take advantage of an OA border bounce to extend my visa.

I have an OA visa (sticker) that is valid until Sept 11 and an ‘admitted to’ stamp with a final date of Sept 24. I checked at the immigration office in Chiang Mai and the officer stated that I can meet the financial requirements for an extension of stay by seeding my account with 800000thb by July 24. I will have the funds in my account on July 23. The TM 30, Thai health insurance, lease, etc are established.

Clearly I cannot have a bank document of proof generated on Sept 23 but I understand that it can be generated up to 7 days prior to the application. My bank book and copy of Sept 23 would show that the funds are current. Is that correct?

An error would be disastrous - a denial would mean no recourse but to immediately leave Thailand. Yikes.

Is there anything I am missing? I will take my paperwork to immigration a week before application to be sure I have it right.

You all provide a terrific service. Thank you.