Crewing is a scheduling problem wearing a recruitment costume
Every vacancy is a date and a port, not a job description
A principal does not ask for a Second Engineer in general. They ask for a Second Engineer joining a product tanker at Jebel Ali on the eighteenth, relieving an officer whose contract ends that week. The date is the requirement. A nomination that arrives two days late is not a slower success, it is a failure, because the relief still has to happen and someone else will do it.
That is why a crewing desk needs a sign-on calendar rather than a pipeline of opportunities. Ninety days of confirmed joinings, laid out against vessels and ports, shows a crewing superintendent exactly which weeks are exposed. Vacancies without a confirmed nomination inside their lead time are the only list that matters on a Monday.
Availability changes underneath you
A seafarer who was available in March has joined another vessel by April, or has decided to stay home for a family reason, or has let a course lapse. Availability that is recorded once is fiction within weeks. It has to be a status that people update, tied to a sign-off date and a stated readiness date, so the pool you filter is a pool that could actually sail.