Seek review before the change takes effect, especially when the employer, professional duties, or work arrangement will change. Give counsel the proposed date and the current I-94 expiration. Do not assume a pending request authorizes work for a new employer.
Bring the decision forward in the business process
Ask HR to involve the immigration contact when the transfer or offer is proposed rather than after payroll has switched. If employment has already ended or changed, report the actual dates accurately and seek prompt advice. The appropriate next step may depend on current status and what has already occurred.
A general article cannot establish an individual grace period, filing deadline, or lawful new start date. Deadlines are not the only calendar constraint; the limits of the route are. TN rests on a temporary purpose, so a change presented internally as indefinite or permanent invites a different question from the one the employer expected to answer.
Equally, remaining validity on an I-94 does not stretch to cover a different employer merely because months are left. Hypothetical example: an epidemiologist whose funded project ends early is offered a place on a differently funded programme at the same institution, and the useful question is whether employer, duties and temporary purpose still describe the admitted arrangement, not how much time remains. Put that to counsel while the transition is still being negotiated.