I didn’t know that the 9 had two jump seats until I went to dispatch a full flight some years ago,to my surprise there were 4 on the flight deck ,a F/A on staff travel was sitting behind the Capt on his Nav bag !!!,you may remember this great character “FF” ,I think he was driving Tug boats on the Brisbane river last time I heard of him..
“The Aircraft is full and so is the Captain”