As I understand it, all of those things could have contributed or not, depending on what ultimately caused the accident. So you have to wonder why the family would sue after the medical examiner said that the rebreather didn't have a dangerous design flaw. That makes no sense. Once the family knew that the rebreather itself was not to blame, I don't see why they would sue. Though I have to ask, how did the medical examiner know this?
And weren't Mrs. Skiles and her children and her lawyers knowledgable enough to examine the rebreather on their own to figure out that it didn't have a dangerous design flaw? You would think any competent family member or attorney for a diver would be able to do this. They should have assumed that the company wasn't hiding anything, because companies never do. That much we have learned from history.
Frankly, it's just weird that the family would even want to know whether the manufacturer itself knew of any dangerous flaws with the unit. I understand that they could only learn this information by suing (and examining the company's internal communications and asking the company questions about its design and testing); but what a waste. After all, it turned out that nothing was wrong. So why did they want to investigate in the first place?
I think the key here is that the family lost the suit. That shows it was frivolous from the start.