General trade experience does not, no matter how strong it is. The knowledge must be of the petitioning organization's own product, process or procedures, or an advanced level of knowledge of its processes, rather than skill that transfers between employers in the industry.
Ask what the employer built, not what the worker learned
The question is best approached from the company's side. Something the organization developed, refined and kept to itself can support the category; something the industry shares cannot. Solomon's kiln-drying control process qualifies as a candidate because the group wrote it, tuned it against its own species mix and equipment, and never released it.
His millwright competence, by contrast, would let him work at any mill in the country, which is precisely why it cannot carry the petition. A useful test is to ask who else could be sent. If the honest answer is that another experienced tradesperson could do the job after a normal handover, the petition is weak.
If the answer is that only a handful of people inside the group understand the control logic and the reasons behind it, the file has something real to describe.