In response to your original question it shouldn't make too much difference. If the spoke is too long the nipple will travel partly passed the thread meaning less of the spoke thread is engaged making the joint slightly weaker. Depends how much it sticks out once you have tensioned it.
Probably better off using 1mm too short and longer spoke nipples. 12mm nipples are often used but if you get 14mm ones then you will have no problems.