Long is good. That means the OS is great. Thanks for pointing out the length of the trial.
The trial reached the designed OS final analysis around summer of 2017. NWBO extended because they wanted longer data.
About 4 years ago NWBO PR'd the trial was finally sufficiently mature to analyze it The 4 multi-month clock was started!.
The delay since then has nothing to with patients living longer. Is about NWBO playing whatever game they are playing with delivering results and going for approval.