Preparation or a pending request does not authorize the proposed US employment. The applicant must have a valid basis permitting that work before starting it. An existing status may have limited conditions; do not assume it covers the new employer, the customer installation or hands-on training.
Match the start date to the completed immigration step
Give the employer a list of outstanding evidence and the actual procedure being used. A contract deadline is not an approval deadline. Consider whether another authorized worker can cover the installation while the case is assessed. Travel for a different permitted purpose needs its own review and must not be used to begin employment before authorization.
Because TN requires prearranged professional activity and bars self-employment, verify that any preliminary calls or site visits do not become productive services before admission or other authorization. Keep copies of everything the officer retains, and note the admission period stamped or recorded, because the renewal calendar starts from that date rather than from the start date the hospital chose.
The safe sequence starts with a written confirmation that the duties fit a listed profession and the credential limb is satisfied; for a diploma-plus-experience case that includes collecting the employer letters, which can take weeks if a former employer is slow.