Legal consequences of AD's / ND's?

Depends on who witnesses it, and what they choose to do about it. If nobody sees or hears, it didn't happen.

There are laws defining where a firearm may be discharged. Accident or not, it's a discharge. The charge is therefore at most discharge of a firearm in [ wherever it's not legal to do so ]. Energetic young socialists will be very keen to use the opportunity to disrupt your life and further their political agenda by adding additional charges such as endangering lives, etc. The legal consequence may be what Julius is facing for doing the same thing intentionally. Except for him, they will quietly lose the docket.

Reasonable people will treat it as an accident, not involve the police, and move on.

Maybe I am the odd one out, but I personally think that there should be consequences for having a ND.

We all know that AD's are very few and far between. If you have a ND, you screwed up. At the very least there should be a course on the rules of safe firearm handling.

How do we discern between a ND and an AD? 

A ND could have been prevented. an AD happened without intent or prior knowledge? 

Please judge these examples:

A. Reholstering a handgun and the trigger snags on clothing, activating the trigger. 

B. Picking up a handgun and accidentally misplacing the hand, activating the trigger.

C. Falling down during a shotong match and activating the trigger.

C is the only one in the list that you could  argue as being an accident that couldn't be prevented with reasonable care. Holstering should be done slowly and deliberately with eyes on the job at hand as should picking up guns. Unintentionally firing a shotgun on a course of fire as a result of falling while on the move is a scenario where I could see myself giving someone a pass.

The idea that every mistaken action with a firearm must have immediate social consequence is unrealistically simplistic. 

Not far down that road is Socialism, where people are not reponsible for themselves, the collective is, and will determine 'consequence' for you.

I have seen people make the same mistakes over and over again. They only change if there are consequences to deal with. I do not want to be the consequence of someone else's mistake.

You shoot your bed or cupboard, etc., I can live with it. At least you pointed it in a safe direction when you screwed up. You shoot my car, house or even the ground close to me or mine, you would need to be very good with your excuses for me not to give you up. If you do it trying to show off, a few years in jail should sort that out.