I'm curious, let's say if they deny the monthly method for the first extension, would it be possible to use the monthly deposits from the previous year to qualify, without also depositing in the current year? Or do the monthly deposits need to continue up to the date of the next/upcoming extension?
you likely got an under consideration stamp, and had to return in a few weeks to get the full extension inked in. Once the under consideration stamp is given it's pretty much a given that the extension is approved.
Highlight the relevant transactions in your bank statement. Include a brief cover letter explaining your work, portfolio, and experience, goals in Thailand.
BTW, your Visa is good till August 26th next year and you won't be able to change to a Non 0 in country till after that date by exiting Thailand and re-entering