The letter you are talking about just gives a date 90 days from the new extension date. Doesn't mean it has to be returned on that date, or even returned at all as there is no record made or receipt given for it's return. The last time I returned my letter I just dropped it off at the door, didn't even go inside. This is at Jomtien office, may be different at other places, same with the joint bank accounts. One size does not fit all.