I am so sorry for your loss and the obstacles you have encountered  What they mean is that the letters become what the law calls "stale" after a certain point in time.  You do not have to go through the entire probate process again.  You just have to pay the probate court the fee for an updated copy of the letters testatmentary with you listed as the executor.  The bank is just making sure that you are still able to act and have not been removed.  Good luck.