The Administrative Office of the U.S. Courts has one list of “current judicial vacancies” (those that exist now) and a separate list of “future judicial vacancies” (those that will exist at some point in the future). It’s sensible for some purposes to keep the lists separate, but the distinction sometimes leads to a confusion.
To dispel that confusion: It’s entirely proper for a president to make a nomination for a future vacancy and for the Senate to confirm that nomination before the vacancy actually arises. (Indeed, when the incumbent steps down “effective upon the confirmation of my successor,” that is the only way to proceed.) What the president can’t do before the vacancy arises is make the separate post-confirmation act of appointing the individual to the office.