I am currently in Saigon on a 3 month extension, there is a stamp in my old passport. Last week I received a brand new US passport because my old one has only 1 year left. (Quick turnaround at the consulate, only 8 business days, much faster than if I did it in the US). I picked up the new passport, and the old one, but they punched holes and wrote cancelled on it.
I have a suspicion that I am not done. That I need to move that stamp or get a new visa in my new passport. Who knows?