The most expensive misunderstanding we see: a company reading its quota as a number of people rather than a number of people in named categories.
A company came in last year with eleven signed offers and a quota it believed covered fourteen workers. On paper the number was fourteen. In practice it was fourteen across four job categories, and nine of the eleven offers were for a category that had two places left.
That is the single most common and most expensive mistake in this subject. A quota describes categories, not bodies. Two carpenters and a foreman are not three of the same thing, and a slot that lapses in one category does not become available in another.
The second thing companies get wrong is timing. Slots do not sit still. A permit that is not renewed releases a slot, and a renewal begun late can mean the slot is gone when the file finally arrives, occupied by the new hire somebody else in the office arranged the same week. Two departments hiring against one quota without a shared list is a problem waiting for a month end.
What we ask for at a quota session is boring and it is the whole job: the registration papers, the current staff list with job categories as they are written on the permits, and the expiry dates. From those three things the sequence writes itself, and the sequence is the answer. Doing step four before step two is what costs a month.
The practical advice is shorter than the explanation. Before you advertise, count your slots by category. Before you make an offer, check that the slot is free on the date the person can actually start. And keep one list, in one place, that anybody in the company who might hire somebody is required to look at.