I'm sure they have an internal schedule and target window. But like every other major project, things happen that cause delays.
We're all engineers here, and we all know that Murphy works on every project. You can't predict what he'll do or need. Maybe an investigation(s) or adjudication(s) takes longer than expected? Maybe it takes too long for SMEs to respond and document an issue, or a meeting of external experts need to be convened? Or maybe IT issues come up? I honestly don't know and I don't think anyone outside of the organization really knows either.
But what I do know is that they won't release the results to the State boards until the entire process is complete, correct, and defendable. The part that that the exam-takers actually see and care about is a small part of the operation.
There's also some utility in not publicly announcing things. Too much potential for backlash if things are delayed. Even last year, when we all *knew* what day it was going to release, they still didn't say publicly that it was going to happen that day. Just the usual "6-8 weeks".