Headcount is not the test, but it is evidence. What matters is whether the duties are primarily managerial or executive, which can also be satisfied by managing an essential function at a senior level rather than by supervising staff.
Function management is a real route, and a demanding one
There is no minimum number of subordinates in the standard, and a claim built on managing an essential function is legitimate. It is also harder to document, because the function has to be genuinely essential to the organisation and the applicant has to be operating at a senior level within it rather than performing it. A production function managed at a senior level looks like setting standards, choosing suppliers and processes, allocating capacity and being accountable for results. A production function performed looks like running the equipment. If the answer to what does he do all day is largely the second, the petition should either be rebuilt around different facts or the assignment redesigned before filing. Deciding this at the drafting stage is far cheaper than defending it later.
Hypothetical example: an optical-coating plant names its production head as a manager, yet she personally calibrates every line because no supervisor has been hired. A first review converts the org chart into a weekly-duty ledger and identifies the decision that must be made: hire and delegate, delay the move, or use a different classification. It also confirms the transferee's continuous qualifying employment during the three-year lookback. Titles and a future hiring intention cannot replace current facts. Where a function-manager claim is used, preserve budget, policy and senior-level authority records that show management of the function rather than personal performance of it.