I don’t know the answer. My guess is in the past the exam committee would have a meeting to approve the exam result, and they usually have 1 meeting that would approve all exams. In the past it wasn’t an issue, but this year I guess they probably met after new years and approved MAS results, and then in a couple weeks they would held another meeting to approve 5-9 results.
For one reason or the other they probably didn’t have a meeting in Dec, or maybe they didn’t want to do so before the exam window formally closed.
Again, I have no knowledge of the working of the CAS exam committee. The guess is based on my past experience with various (non CAS) committees.