Training history, role descriptions, project records, internal materials, organizational letters, and evidence of the employee's use of the relevant knowledge can help. The selection should protect legitimate confidential information while remaining specific.
Use examples that a reviewer can verify
A strong explanation traces the knowledge from development to application. It might show unusual product configuration work, internal system access, documented training, a limited group of similarly trained staff, or responsibility for a method integral to a service. Use redactions carefully so the remaining material still makes sense.
Letters should identify authors, sources of knowledge, and factual bases. Generic statements that a person is indispensable are weaker than examples tied to actual duties. Build the record from contemporary, verifiable documents rather than a summary written for the filing alone.
Names, dates, ownership percentages, duties, payment trails, and addresses should be capable of being reconciled across the file. Where a document requires explanation, provide a direct explanation and keep the underlying record available. Translation, credential evaluation, or professional evidence may be needed depending on the particular category.
Keep a contemporaneous record of the decision and the facts used to reach it. When a document is unavailable, identify the reason and consider whether another primary record can establish the point without creating a contradiction. A later change in role, ownership, family circumstances, or planned activity may require a fresh review.
Clear disclosure is more useful than an attempt to make facts appear simpler than they are.