In Bangkok you can have the bank letter (and the year detail transaction report) dated up to a week before you apply for your extension. The only requirement they have is that you need to update your bank book on the day you apply
@George *******
your mistake is listening to your bank, NOT your immigration office..
Although I will admit there are a few offices that make you get the letter on the day you apply for your extension.
What office do you use for your year extension?