I just managed to get a 3 TN through a new employer. The officer at Peace bridge although approved our 3 year TN, yet he didn't specify that date with those on I-94s that he issued since he was of the view that the TN can be valid firstly as much as the duration of the main applicant's valid passport and then later based on each dependent's valid passport . Hence myself and my kids got it for 2 1/2 and my wife got it for 1 1/2 year. He told us that when we renew our passports, we should come back, pay $6 a piece and get another I-94. I am not sure if this is the correct process or the officer was misinformed since we now have to go to the border alteast 2 times to renew the TN, firstly for my wife and then for the rest.