I think at any one point they will have 4 different ships undergoing some kind of construction/trials, so there will be a lag between any design changes and the flow through into the planning/scheduling process. Minor tweaks to things that are done in the module stage (like where a pipe bracket goes) are relatively easy, but would take a while to actually get implemented in the build because of far ahead some of that is done. I think by the time we figure out some of the issues on the first of class while on trials, it will already exist on 3-4 more that are in production, and if they are major issues it will take a while to engineer the fix.
So even if we do the contracting in batches, actual changes may not flow through like that.
Bit different than the older method of building from the keel up, where you were basically working on one ship at a time (and maybe starting some of the preliminary work on forming/cutting the plate for the hull). Modular building should give you much better consistency between ships, but also means that you get the same defects passed through (consistently) and there is a bigger impact when you want to make changes, because you have a lot of concurrent activities on the go that affects multiple hulls.
For example, flagging issues on HDW right now, but they are also on MGB, and at least two other of the in construction AOPs. The solution may make it into the sixth ship baseline design, and hopefully implemented on 4 and 5 as design changes before delivery, but probably will have at least 3 ships with the same first of class issue. If it's a docking dependent repair, they run like that for the full 5 year op cycle. Don't worry though, the original design was approved by a class society, so there won't be problems....
Pretty funny to see DND defer to class society opinions over our own SMEs, despite the fact that some of the surveyors have no specific expertise, and some of our people have decades of it.