A position is a staffing slot; a worker is a person. An open position can have no incumbent, and an active worker can reveal an assignment defect if another worker references the same position ID. Counting worker names therefore doesn't tell you how many positions are vacant.
Use position status and the incumbent relationship together. Open and Closed are different states: a closed position isn't a vacancy to recruit for. Compare stable IDs before calling two similarly titled roles duplicates. In Northstar's records, there is a deliberately inconsistent assignment to investigate later. Your job here is to expose the underlying rows clearly enough that another analyst can check them.