One of the problems with a safety system is that when you find an omission/error/oversight/process concern you (should) start to wonder what else has gone wrong or been missed. if I were the FAA, I would be taking a big sample of other sign-offs and having a really good look at them. This MCAS affair has cast doubt on the integrity of a Organisation's Management System; that's going to take a lot to address and far more than a software tweak.