In client_bulk.py, the following logic is used to determine whether to use the final write concern (set to w=0 in the case of unacknowledged bulk writes) for the final bulkWrite server command. However, this condition does not represent the final bulkWrite batch. For example, if there are 10 InsertOne ops of size 16MB then this condition is true, but multiple batches are still required.

while self.idx_offset < self.total_ops:            
# If this is the last possible batch, use the final write concern.            
    if self.total_ops - self.idx_offset <= bwc.max_write_batch_size: 
        write_concern = final_write_concern or write_concern