Uniqueness is not an independent, universal requirement. What matters is whether the evidence as a whole shows qualifying special or advanced company knowledge connected to the proposed U.S. duties.
Support the claim rather than asserting it
Identify what the employee actually knows, how it was learned, and why the U.S. assignment needs it. A broad claim that no one else could do the job is less useful than a concrete account backed by training records and project history that a reviewer can check.
Begin with a knowledge map rather than a résumé. Identify the company-specific process, how the employee acquired it, the evidence that the knowledge is not merely common industry skill, and why the U.S. assignment needs that person. Hypothetical example: a vial-filling calibration engineer knows an internal method for reconciling sensor drift across proprietary equipment, but the support letter only says the engineer is experienced. The company should decide whether it can document the particular knowledge and its business relevance. L-1B also rests on qualifying employment abroad for one continuous year in the three years before filing, and its maximum period is five years.