Internal documents created in the ordinary course: validation and commissioning reports, procedure revision histories, training matrices, project files and correspondence identifying the employee as the source of the knowledge.
Prefer records nobody wrote for the filing
A director’s letter asserting that an employee is uniquely knowledgeable is expected, and it is corroboration rather than proof. The documents that persuade are the ones the company generated for its own purposes before any transfer was discussed. A training matrix shows who was certified on what and when. A validation report signed by the employee shows responsibility for a process. Revision histories on standard operating procedures show authorship. Internal messages show who was consulted when something went wrong. Assemble those first, then write the letter around them. Commercially sensitive detail can be handled sensibly, and French-language records filed with USCIS require complete certified English translations.
Assemble corporate relationship evidence, foreign employment evidence, and specialized-knowledge proof in separate folders before combining the narrative. The strongest technical evidence shows what the system is, how the employee learned it, and why the U.S. work needs that particular experience. Avoid unsupported secrecy claims. Compare job descriptions with contemporaneous project material so that the same knowledge is described consistently. Hypothetical example: a prosthetics manufacturer relies on a training certificate alone; workshop notes and product-validation records better explain the claimed company-specific technique.
Ask technical managers to identify the author, date, and project for each internal record, because an undated description is harder to connect to the employee’s claimed knowledge.