It seems the terminology is constantly changing on this, I was brought up with ND being an AD, and AD being 'misfire'. But there are many types of misfires, mechanical failures and slam fires. I, in fifteen years of shooting, have never witnessed a mechanical failure of a weapon system that led to misfire or a round being discharged. I've heard from a few primary sources about slam fires on various rifle platforms, but never on handguns. I'm sure someone like MB would have the shooting experience, to enlighten us.
I wouldn't be worried about it, you could remind the wife that cops leave their chambers loaded for literally months at a time with the the same round in the chamber without the hammer falling. The true misfires are probably so few and far apart that no one keeps those numbers, and even if those statistics were kept, you would only being seeing those that were reported to a manufacturer.