The airlines thought they had the warning light. Boeing thought they had delivered the warning light all airlines as a default. It was only later that Boeing d

The airlines thought they had the warning light. Boeing thought they had delivered the warning light all airlines as a default. It was only later that Boeing discovered they messed up and had made the warning light dependant on another feature which was optional. And then Boeing didn't tell airlines about the broken warning light until just a few months ago.