Foster would be used for initial tests to see if a new idea is even worth continuing. As programs progess, they end up in operational testing. How does this thing actually perform in the working fleet environment? Yards also develop all the techniques and steps they'll use to install the system en-masse, and set up supply chain networks, etc. All these programs are independent of each other; on their own schedules and funding, etc. Once each has satifactorily completed all phases, then it's "released" to the fleet. Integration of any two given systems, like SPY-6 and AN/SLQ-32(V)7, is among the last steps. First, each individual system needs to be validated. That can take years.

As you point out, Pinckney only got her cheeks shortly before Lucas. SPY-6 was then just beginning its operational testing, while the SLQ-32 system then had a "leg up." No way would they be together on the Lucas. As far as not yet completed Flight III without cheeks, the yards are only just now "getting the rhythm" for mass installation of those cheeks. Flight IIIs are not even to that stage, and the version of SPY-6 that will actually go on a IIA is a variation of the one on the IIIs. More testing. Not as extensive as if it were a new system, but some testing all the same. Plus supply chains, etc.

Both the future supply chains and the future IIIs need funding, and that item falls under Congress' schedules, and National Defense budgets, and politics. The money is often released in stages. This year, we authorize the keel, and proclaim a name. Next year, we'll fund weapons, and then electronics after that. If you look, annual budgets will actually have things like, "$XX for four SPY-6 radar sets for DDGs 128-131." It gets that specific. The Navy then can't buy any more of those sets that fiscal year, and may only use those sets on those specific ships. The same budget may not authorize any new SLQ-32 systems that year, or authorize those which are purchased for other hulls. Most folks, even here in this country, have no idea how much influence (negative and positive) Congress has on the composition and running of the Navy.

So, while it is surprising to you, having this (actually very limited) knowledge of how our acquisition system functions (or fails to function,) it's not really that surprising.