They should clearly identify the source of their information and avoid claiming direct observation they did not have. Authentic company records may provide context that needs accurate explanation.
Distinguish a records-based statement from eyewitness evidence
Specify the relevant period and the applicant’s contribution. Do not backdate a letter or attribute a project to the applicant merely because the original supervisor cannot be contacted.
Provide enough context for a reader to understand what changed and why. A transition memo or handover document prepared when the new manager arrived can describe institutional knowledge about the applicant's prior work without pretending to be an eyewitness account, provided it was actually written at that time rather than reconstructed later for the application. Look for a colleague who overlapped with the applicant during the earlier period and can speak from direct experience, since that person's account carries different weight than the manager's secondhand summary. Where a performance review or project retrospective already exists in the employer's files, cite it as what it is rather than rewriting its content in the manager's own words, since the original document's date and author matter more than a polished restatement. Keep the manager's own statement limited to what the written record and available colleagues actually support, rather than what seems plausible in hindsight after the fact.