@Will ***********
And that is how, unless you have a bank account and 800K THB in it from before, most people do their 1 year extension, from within Thailand.
Enter Thai on 90 days Non O visa, open bank account, transfer money to season for 2 months and apply for 1 year extension of stay from within Thailand. That is where international transfer flag comes into place. Subsequent extensions do not require that (say, money from 800K withdrawn down to 400K and topped up back to 800K) does not have to show as international transfer.
Just my understanding from 1000s of posts here.