Thank you for your interest in our shared task. And for sharing your questions on this forum.
Re-Q2: Yes, the value for each annotator_id is a list of integers, not a single integer. In PDIS, annotators were allowed annotate the same item (markable or in this case, mention) more than once. We provide all the annotations given by the annotator for any given item.
Re-Q3: Yes, it is a slip in writing, I'm sorry. We meant "...probability of the mention belonging to each of the two classes". We'll correct that.
Re-Q4: You may decide to focus on a single task, and propose a disagreement-aware loss function that works for that task alone. If you do this, you will not win the competition but on the leader board for that task, you will come out on top.
To win the competition, your novel approach to learning from crowd annotations must have best average score across all the tasks.
I hope this response answers your questions. If not, please feel free to ask for further clarification.
Thank you.