Two files. One holds the technical record with dated versions and authorship; the other holds every prior admission, departure and approval notice bearing on the five-year limit.
Two files, reconciled against each other
The technical file should contain the control logic and commissioning schedules as internally recorded, earlier versions showing development, the field data and test results behind them, internal training material, and correspondence approving changes, all connected to the named employee. Add a written comparison with commercially available systems, explaining what the company knows that the market does not. The time file should contain passports with entry and exit stamps, electronic arrival and departure records, prior approval notices, and any employer letters covering earlier U.S. work. Reconcile the two sources against each other, because they frequently disagree, and note absences from the United States during any prior assignment. Support both with ordinary corporate evidence: incorporation and share records, financial statements showing both entities trade, and payroll for the qualifying year abroad.
Where confidentiality limits what the employer will release, agree in advance on a substitute that still settles the point: a redacted document, a description of the system prepared by someone senior, or a statement from the person who supervised the work.