How does immigration verify the 800,000 baht requirement for visa extensions in Thailand?

IF when you got your yearly extension you were not given a paper with a date stamped on it 90 days out saying to update your bank book and come back on that date you don't need to do it at all. Your immigration office will look at the balance NEXT year when you apply for your extension and make sure you met the requirements.

I think there is only one or two immigration offices that are handing out that "come back in 90 days and show us your bank book" document. One is Jomtien and I think there's one up in Isaan that does it too

This is what the document looks like IF you have to go back in 3 months.