For the monthly method my understanding is that your 1 year Thai bank statement must show that you have deposited at least 65,000฿ each of the previous 12 months into your Thai bank. The deposits have to show that they originated outside Thailand.
I believe you have to use the 800,000฿ deposit method for the first year extension and then you can use that year to establish a record of monthly deposits
Also, by verification letter, I mean what is often called the bank letter which just states that you have a valid account, the account number, and the account balance at the time of the letter. It doesn’t address something like monthly income.
Several major embassies, including the US, stopped issuing income verification affidavits in 2019. Since then you get a account verification letter from the bank and a 1 year bank statement plus your bank book with a same day transaction. You don’t need anything from the US embassy to get a 1 year extension at Bangkok Immigration
The pink ID worked for buying a motorbike. Lots of people think it is useless. Whatever. I was after the yellow book and the pink ID was immediately available so I got it.
I got a yellow house book in Sisaket province which can serve as a substitute for a foreigner residency certificate. Getting the yellow book was a bit of a process involving my Thai wife, her family, and the village headman. Once you get the yellow book you can, in the same office, get the Thai pink card which is what I am calling my Thai ID. It’s not exactly a substitute for your passport but it works in some situations like registering in a hotel or as an ID during police traffic stops.