A factual description of the position, pay and intended period, along with the qualification and identity records the applicant is relying on. Any difference between the offer and a separate support letter should be resolved first.
Let each party confirm what it actually knows
The applicant supplies credential and identity records; the employer confirms the real working arrangement. If a staffing agency and an end client describe the assignment differently, ask them to reconcile the accounts rather than picking whichever version sounds cleaner. Keep dated versions so the current one is clear.
Build a dated evidence list before anyone assembles a polished package. It should identify the person who can confirm the duties, the final version of the offer, the credential records, and any client agreement that affects where or for whom work will occur. Hypothetical example: a prosthetics designer receives an agency letter that names a hospital client, while the client statement says the project is for several facilities. The parties should settle the assignment description and retain the executed documents rather than submit conflicting summaries. A Canadian citizen may seek classification when inspected for travel, or the U.S. employer may use Form I-129; the selected procedure does not eliminate the need for a coherent employment record.