See the note below from US Embassy Ghana:
If NVC has informed you that your case is documentarily qualified and it is awaiting scheduling of an interview at post, then you must wait for NVC to notify you of an interview date and time at U.S. Embassy Accra. Each month, the consular section provides a total capacity for IV applicants and interview to NVC. NVC will schedule interviews at post and send the visa applicant, the petitioner, and the registered agent/attorney an email noting the date and time.
Since March 2020, the COVID-19 pandemic has dramatically affected the Department of State’s ability to process immigrant visa applications. U.S. Embassy Accra has resumed visa services as expeditiously as possible in a safe manner, however, operational restrictions and staffing shortages over the past years has greatly limited the number of IVs the consular section has been able to process. As a result, there is a large backlog of documentarily qualified IV applications waiting to be scheduled at post Accra. IV applications are scheduled and interviewed according to priority date. We thank you for your patience and understanding as we work to resolve the IV backlog in a manner that is fair to all applicants and recognizes the hardship that has been placed on all separated families awaiting their turn.
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What's the context of priority date here? Is it pertaining to other visa categories or the actual NOA1 date?