Product or process documentation marked proprietary, design documents and version histories showing the specialist's authorship, internal training records where she taught others, project logs where issues were escalated to her, and a manager's statement with numbers rather than praise.
Version control and training records beat praise
Specialized knowledge is proven by the company's own artefacts. The strongest exhibits are ones that already exist and were not written for immigration: a repository history showing the specialist authored the integration modules, internal wiki pages she maintains, training materials she delivered to new hires with attendance records, and support tickets that show colleagues escalating to her. Hypothetical example: a Shannon training-systems firm can add its scenario-format specification with a proprietary notice and a table of the projects where the specialist led integration.
The manager's letter should then state how many people in the whole group can do the work, how long the internal training path takes, and why the Florida subsidiary needs the knowledge now. Around that core sit the L-1 basics: her contract and twelve months of payroll from the Shannon entity, share registers linking the two companies, financial statements and contracts showing both operate, and, for customer-site work, the agreement proving the petitioner controls her assignments. Translate French materials.