Skill in actuarial modelling is general; knowledge of the company's own proprietary model, its assumptions and its integration is specialized. The petition must show the second, not the first.
Draw the line between the field and the firm
Hypothetical example: a Quispamsis insurance back office describes its analyst as one of the best reserving specialists in the region. That is praise, not evidence. L-1B specialized knowledge is knowledge of the petitioning organization's product, service, research, equipment, techniques, management or other interests, or an advanced level of knowledge of its processes and procedures.
The analyst qualifies if he knows the company's proprietary reserving model, its undocumented assumptions and its data dependencies in a way that a newly hired actuary could not acquire quickly. He does not qualify merely because he is highly skilled. The petition should therefore describe the model's proprietary elements, the years he spent building them and the time it would take to train a replacement.
Comparing his knowledge with that of other employees, and explaining why only a few people hold it, helps the officer distinguish the firm's knowledge from the profession's.