The max attendance is expected for Nets basketball games, with 16,500 expected--presumably accounting for no-shows despite official sellouts. (The arena seats 17,732 for basketball.) The 14,000 expected for Beyonce is either a lowball figure or based on a concert configuration that puts certain sections out of commission.
Note that in 2012 the arena expected 14,000 for Andrea Bocelli, but now expects 10,000. Tickets are on discount.