It should not. The category can rest on an advanced level of knowledge of the employer's processes and procedures, and there is no general requirement that knowledge be unique or proprietary. What matters is the depth described and its connection to the assigned work, not whether others have been shown the basics.
Describe depth, not exclusivity
Write the claim so it would still stand if a reviewer knew that thirty colleagues had attended the course. That means naming the judgement, exception handling, and design decisions sitting above the taught material. An argument built on nobody else knowing this collapses the moment the training records appear, and the training records are usually in the file already.
Depth survives that discovery; exclusivity does not. Two further points keep that claim within its proper limits. The standard offers two ways of framing the showing — special knowledge of the employer's products, services or their application, or an advanced level of knowledge of the employer's processes and procedures — and a case does not have to satisfy both, so choose the framing that fits the facts and argue it properly rather than gesturing at each.
And note that L-1B stay is capped at five years in total, with prior L time consuming part of that, which is worth establishing before a training programme is planned around a longer horizon than the classification allows. Hypothetical example: a curtain-wall detailing specialist frames the claim around the employer's own tolerancing and sequencing procedures rather than around a widely used drafting package, and the account is both narrower and considerably harder to answer.