The impression I got from the text is that Boeing has steadfastly denied a coverup, and there is probably not enough evidence to convict if they were to take them to court. The earlier crashes, the ones that claimed lives, sound like they haven't been reclassified to include this as the cause. The only incident that specifically ascribed to the control valve is the one where the pilot regained control and there was no actual loss of life. That allowed the FAA to determine the cause, and force the changes, but it didn't allow them to retroactively change the cause for past crashes. (something undoubtedly Boeing would have fought.)