Driver Line-up

I was a bit confused by the driver line-up switches between races. Simon Dolan recovered and completed Spa 2 weeks after the wreck, while Marc Gene replaced Filipe Alberquerqe. They didn't really explain the reason for bringing him in except that he was an experienced driver and mentor. Then when he left somehow they had to bring in Ollie Tirby in order to have 3 drivers? I thought they had Dolan, Alberquerqe, and Tinknell?