Configuration and change histories, authorship records for internal procedures, training materials and completion records, an organizational chart, and a signed statement quantifying how many staff hold comparable knowledge.
Ordinary business records make the argument
The persuasive material is rarely written for the petition. Change logs in the system show who decided what and when. Internal policy and procedure documents carry authorship and revision histories. Training curricula show what the organization teaches, and completion records show who has been taught. Incident or escalation records show which problems were routed to the individual. An organizational chart shows where the role sits and who else does related work. On top of that, a short signed statement from a senior operations or clinical leader, quantifying how many employees could do the work unaided and estimating the months required to train someone new, converts scattered documents into an argument. Anything in another language needs a certified English translation.
Strong evidence starts with the company's actual welding procedure specifications and supporting qualification records, showing the specialist's direct involvement in developing, revising, or applying them, rather than simply listing certifications on a resume.