No universal rule requires knowledge to be impossible to teach. Assess the actual special or advanced knowledge and proposed duties.
Explain acquisition and application
Use genuine training and project records to show what the applicant knows. Do not replace the standard with a claim of permanent irreplaceability.
Identify the specific process, product, or procedure at issue and document how the employee acquired and applies that knowledge, rather than describing general loyalty or years of service as the qualifying fact. Specialized knowledge means knowledge of the petitioning organization's product, service, research, equipment, techniques, management or other interests and its application in international markets, or an advanced level of knowledge of the organization's processes and procedures. Specialized knowledge must relate to the company’s products or reflect advanced command of company processes; familiarity with an obsolete version does not prove mastery of a replacement, yet unchanged expertise need not be discarded. The reviewer needs enough substance to distinguish company-specific or advanced knowledge from ordinary industry competence, while sensitive material can be redacted or summarized responsibly.