Well, there could be one explanation to which I have hinted before: possibly, some of the resources are getting shared between SCs in order to even out the processing dates.
I don't think mailing 10,000 I-485 applications from Nebraska to Vermont is a feasible thing here, but possibly, they are trying to level out these processing dates, so there is more of an even backlog, by sharing people. As much as VSC folk complain here, remember that TSC and CSC (and up to recently, NSC) applicants are in worse situations, as far as timelines.