A recruiter may help draft a support letter using verified facts. The employer must confirm the role and its terms, and the applicant must verify personal history and credentials against the records. Separate drafting assistance from authority to make legal assessments or attest to facts the drafter does not know.
Trace every claim back to a person
Go through the draft package and mark, for each substantive statement, who verified it. Duties and supervision come from the manager. Salary and term come from whoever sets them. Degrees, diplomas and years of experience come from the applicant with supporting records. Anything nobody will own should be removed or rewritten rather than smoothed over, because it is the part an officer is most likely to test.
The employment file is what supports any future extension or change, so it should show continuity: consistent pay, unchanged duties, and the same employer relationship. A description of the agronomic advice, trials and technical support the role delivers, the growers and dealers served, the supervising agronomist or manager, the salary, the duration and a statement that the applicant holds no interest in the company. Treat the employment letter as the central explanation of the TN engagement and the relocation agreement as evidence of a separate private benefit.