No. A travel pattern does not create continuing permission by itself. Canadian or Mexican citizenship, qualifying professional work and credentials, and temporary entry remain relevant. Distinguish a return during an existing authorised period from a request for a new period, and check the current employment facts before each trip.
Each entry is judged on its own facts
An officer at the port considers the case in front of them, using the documents presented that day. If the employer letter is stale, the credential evidence was left at home, or the duties described no longer match the work, the previous admissions do not fill the gap. Applicants who cross often should keep a complete, current set of documents rather than a thinner one that has worked before.
If the deliverable is survey data, plans, boundary determinations or the professional judgement attached to them, the engagement is professional work within the listed profession and the letter is simply badly drafted. State law then governs practice: the hospital's state board licenses nurses independently, and most boards require an examination, a credential verification and a background check. TN remains limited to Canadian or Mexican citizens performing prearranged work in a listed profession with that profession's qualification; a Canadian permanent resident does not qualify by residence alone.