USCIS has clarified their Policy Manual regarding criteria for certain TN occupations as found here: https://www.uscis.gov/policy-manual/volume-2-part-p-chapter-6
Meanwhile, the Regulation listing all TN USMCA occupations appears here: https://www.ecfr.gov/current/title-8/chapter-I/subchapter-B/part-214/subpart-A/section-214.6
