I used the income method last year. I have my US SSI payments directly deposited into my Kasikornbank account. They will provide what’s called a “Bahtnet” transaction statement which is clearly detailed as a payment from SSA with amount and date. As long as they match with your bank statements you’re good.
No worries. I have the same situation extended OA 23Dec, OA expires 7Jan and new insurance effective 19Jan same date previous policy expires. Btw your new extension is dated the day your previous one expires.