That they knew back then that things is going to happen in December could have more explanations than your suggestion. My guess for the specifics in this delay is that the case has been put to court, and they got a court date in December.
But obviously this is just a guess, too.
Have you any suggestions for a rationale behind your theory?
If it is 'ordinary' negotiations, a known time frame from the start seems unlikely, and if they even expected the negotiations to fail, as you suggests, what could they possibly gain by a delay?
I have not kept an eye on the igg numbers, but