reward is a one time only thing. So far I have seen reports that people where able to obtain one extra quest but that is a bug. No reports so far that they actually got the reward for it. besides that having all four quests bugged to re-obtain and have all 4 rewards is very unlikely. plus that their might be a failsafe in the final reward as well.
Cause of the many bugs, I wonder what he last update was about. might be a fix for it...