What documents do I need for the 'O' yearly extension for Thai children with 40k bank transfers?

okay we're talking about THREE different things entirely

1 - There's the year transaction detail report <- that sometimes has to be ordered from your bank 5 days before you need it. It is the one that immigrations refers to because most people don't update their bank book every couple of weeks and it shows EVERY transaction by month so they can see the balance (for people who use banked money) and so they can see the incoming international transfers (for people using monthly transfers)

2 - There's the "standard" 6 line bank letter, has your name, (sometimes your passport) your account, and the balance of the account on the day they wrote the letter. <- This is the one that SOME (not all) offices allow to be no more than 7 days old (some want it the day you apply) 😕

3 - There's the updated bank book <- it has to be updated the date you apply for the extension

Immigration in Maha Sarakham sent me back to the bank because the bank person updated my passbook but Immigration wanted it updated by depositing a token amount of baht in it. May be the same in your case.

You would need a letter from Bank. Some offices accept a letter up to 7 days old, some only accept a letter issued on the day of application. Check with the immigration office in your province. If former, you need to update your passbook on the day of application.