Keep the original offer, professional description and actual authorization alongside the new duties and effective date. The comparison should show the change rather than conceal it.
Explain the revision without rewriting the earlier assignment
Identify what was completed, why the client now wants different work and which responsibilities would be added. Preserve any ownership or reporting changes. Reusing an old client letter with a new date may leave the actual proposal unexplained. Qualification evidence can remain relevant without establishing that the new role itself is within the same profession or already authorized.
A short letter on institutional letterhead stating that the former school merged into the current one on a given date, that the program continued, and that the transcript reflects the same records does more than several pages of applicant explanation. Ask the hospital's recruiter for a letter on letterhead that names the legal employing entity, states that the applicant is being engaged as a Registered Nurse under the USMCA, and describes the unit and duties in clinical terms. The experience must be evidenced rather than asserted, which means letters from former clients or employers describing the consulting work performed, engagement letters, and a record that lines up with the years claimed.