Just the same, there are far more than four flight IIAs.
The Flight IIA batch started with the Oscar Austin, DDG 79. We have now commissioned DDG 101 Gridley, meaning there are now 21 Flight IIAs commissioned. Four more have been launched and are in run up to commissioning so there will soon be 25 of them. Six more are planned with 3-4 of them already under various stages of construction. Ultimately there will be 31 Flight IIAs.
BTW, DDG 100 was commissioned and is named the USS Kidd. The last, DDG 111 will be named Spruance.
As I said, we should most definitely have kept the Spruance class. But the Burke class is a capable ASW vessel, typically mixing one earlier flight and a flight IIA in a CSG, which allows the two helos from the IIA, the two from the Tico cruiser (and many times there are two Tico cruisers) and the five or six helos from the carrier to a very adequate ASW job, using the deck of the earlier flight Burke to refuel and hop onto.