What should I know about obtaining the correct bank statements for visa extension in Thailand?

Unfortunately, in Bureaucrat-Speak (e.g. Banks, Immigration, Embassies), a year is a particular year as distinct from the last 12 months. e.g. 2025 Gregorian Calendar Year or 2568 Laos/Thai/Cambodian Buddhist Calendar year. The same goes for "Decade" e.g. The 2010s c/f to "the last 10 years"; Century and Millenium etc. Visa-speak is even more fun. The following is what I have learnt from this group (and is partly tongue-in-cheek, but I believe it to be true): A "Visa" is simply permission to enter a country under the terms of that particular visa, granted by that country's embassy somewhere. This is totally distinct from a "Permission to Stay" stamp that you used to get when you entered the country. With digital systems, you may not get that stamp in your passport and you must trust it has been recorded accurately (I think some Officers might allow you to look at their screen or give you an actual stamp if asked nicely). You cannot extend a visa. You can extend the invisible "permission to stay". If the "permission to stay" was granted under a Multiple-Entry Visa and is within the time-frame specified in that visa's first permission to stay, that might be for the same period as specified in the visa e.g. 12 months. But the NEXT stamp, or the invisible entry in the immigration computer, will not necessarily be under the same conditions as the original visa. e.g. A Multiple-Entry OA visa for Thailand can be used without a re-entry permit for multiple entries within the time dates specified by that visa as long as the Medical Insurance is still current, and it will be extended for the time period specified. Outside the dates specified in the original visa, however, the conditions of the visa invisibly and secretly change. It becomes a Single Entry Visa and you require a re-entry permit or you lose the right to enter under that original visa. An Immigration Officer is a member of the Police Force and is not some sort of "Customer Service Officer", even though they are called "Public Servants" in many countries. They are not required to tell you anything or ask anything like "Do you have a re-entry permit?" Upon an attempt to re-enter under the terms of the original visa, they will not tell you to go to the counter over there that says "Immigration" and get a re-entry permit, after all - they too are Immigration.