My TN expires in 8 months. How early can i apply renewal via i-129 and how early can i go to the border for TN renewal ( with same employer and position in both cases). Also, does the TN letter need to mention it is a renewal or it will be just like a new TN letter visa ( and check extension category in I 129) or add that information in the cover sheet (I129) or explain verbally at the border( if going to border)?