No. Proprietary or unique knowledge is not a universal requirement, and holding it does not by itself establish the classification. The showing turns on knowledge of the company's product, equipment, or technique and its application, or an advanced level of knowledge of the organisation's processes, supported by facts about the work.
Argue from work performed
A file that leans on the word proprietary usually says very little about the applicant. Replace it with what was done: the process step owned, the problem solved, the internal standard written, the site trained. Note how long the knowledge took to acquire inside the organisation and why it could not be picked up from published sources.
That factual account is what a reviewer can test and what counsel needs in order to assess the case honestly. Test the claim by writing what a competent replacement would have to learn and how long the learning would take inside the organisation. If the answer is a fortnight with the manual, the file is describing a capable engineer rather than specialized knowledge.
If it is a year of exposure to the company's own equipment, procedures, and failures, the description has content a reviewer can weigh. Alongside that, the continuous qualifying year abroad within the preceding three years has to be documented, and the proposed United States duties have to match what is claimed. Where the same facts could support a managerial description instead, ask counsel to choose deliberately rather than blending both descriptions into one narrative.
The maximum L-1B stay is five years.