I-129 Filing Guidance from the California Service Center.
Form I-129 may be rejected if it does not include the required duplicate copy with the supporting documents. The general filing instructions for the I-129 instruct the petitioner to submit the petition with the supporting documentation in duplicate, if the petitioner checked block "a" in Question 5 of Part 2 of the I-129 form. This question concerns the notification of a U.S. consulate or port-of-entry of the approval of the I-129 in the event the applicant is outside the U.S.
Generally petitions for an extension of TN status or petitions requesting a change to TN status will not require this notification as the applicant should already be present in the U.S. However, a procedure is available for TN applicants to file their I-129, depart the U.S., and then re-enter upon the approval of the petition and notification at the port-of-entry designated in Part 4 of the I-129 petition. Presumably the I-129 is not deemed to be abandoned due to the departure because the requested action marked in Part 2, Question 5 of the I-129 is for admission into the U.S., and not for Change of Status or an Extension of Status.