Payroll registers and employment contracts establish the employer and the period; travel and entry records, assignment letters and expense claims establish location. Together they support a month-by-month timeline that the petition can rely on.
Build the timeline, then attach the paper
The most useful single document in a case like this is one the company creates: a table with one row per month, showing the employing entity, the work location, the role, and the evidence for each. Everything else hangs off it. Payroll registers and tax records show who employed the person and paid them. Employment contracts and any amendments show the terms. Passport stamps, entry records and airline itineraries show movement. Assignment or secondment letters explain periods away. Expense claims corroborate where the person actually was, sometimes more reliably than anything else. Where a period is genuinely unclear, saying so in the timeline with the best available evidence is far better than smoothing it over, because a discrepancy discovered later damages the whole file.
Hypothetical example: Simon, an executive at a Canadian laboratory-supply company, is being transferred to its U.S. subsidiary. The first review should match each required fact to a record: tax filings and invoices for doing business, share records for ownership, payroll for the foreign year, and organizational charts for the two roles. A support letter should explain the documents rather than replace them. He should gather records while former supervisors and corporate signatories are available, because an affidavit prepared later rarely settles a gap that payroll or board minutes could have answered. The filing sequence should follow the evidence map, not the order in which documents happen to arrive.