Do not assume permission for one proposal covers different U.S. employment.
Assess the intended interim work
A future start date or pending application is not general work authorization. Review the actual activity and present status before beginning.
Hypothetical example: an acoustical-engineering consultant learns that a museum installation moved by six weeks and is invited to perform unrelated procurement work in the interim. The person should identify the new duties and location before accepting them; the original professional proposal does not automatically cover the substitute work.
For TN, confirm citizenship of Canada or Mexico, a listed professional occupation, the required qualifications, and a genuine temporary employment arrangement. A Canadian citizen may seek admission at a designated inspection location or preclearance, while a U.S. employer may submit a Form I-129 petition to USCIS. Neither path permits substantive self-employment through a U.S. entity the applicant controls.
A timing review should produce a sequence of facts, not a promise. Mark the commercial event, evidence deadline, government filing or application, requested validity period, actual admission or approval, and any activity planned during the gap. Ask what permission supports each activity while physically in the United States. A revised project date can require new evidence or a new decision, and it never silently expands the scope of authorized work or residence.