I called Ho Chi Minh Embassy and spoken to the lady: the amount 500,000 baht must be a current statement in a normal bank or saving account, with the 6 month statement, not necessary with consistent 500,000 baht in 6 months. But the consular will consider based on your transaction within 6 months to verify the validity and the purchase power
I have them consistently over the past 6 months and I heard some embassies require it to be in for 2-3 months. I did not hear anything like that from my application and other applications from this embassy (but it does not mean they don’t require it)