back in 2014, theire was a problem with Arenas of the Darmos Games
where the Optional task (task 3) actualy counted for success chance
viewtopic.php?f=5&t=40672but Dan fixed that, and checked up on both The Cerulean Conclave and Carjean the heist
so as far as anyone can tell the text in patch nodes is 100% corect now
Quote:
* Optional/Side Objectives - some missions have tasks that do not contribute towards the success or failure of the mission. They should generally only be chosen once the mission has already achieved a satisfactory chance of success. Contributors to these tasks will still be eligible for mission success rewards as if they had participated in a normal task. The mission will indicate if it has optional objectives.