For vehicle usage we use lugs to connect to 12awg (or thicker) that easily handle 23A. Standard connectors used in our applications are Anderson SB50 and there's no issue at all with 23A. Typical wiring is automotive with appropriate insulation. Not sure why you are fixated on 12awg anyway. Most of us are running 10AWG or 8AWG or thicker depending on current carrying and length of wiring. This kind of wiring has insulation that is well rated about 90C maximum. Though I doubt anyone would be running 20A+ and not size wiring appropriately.
NEC ratings are typically looking at wiring in conduits, home wiring etc. This is automotive where we aren't running solar wiring in large bundles and along the exhaust system or inside walls... Cables are typically just in a sleeve and with plenty of air around them.
Fuses/circuit breakers of course are a smart thing to use in any wiring, especially vehicle.
Anyhow, glad you're looking at absolute worst case scenarios. Panels (at least the kind we use) have diodes to protect against reverse voltage (primarly to prevent battery discharge back into the panels at night), so even if one panel had severe shorts it would make no difference to other panels that are connected in parallel - no appreciable current will flow into the damaged panel.
All pretty moot given the majority of us are using 100W or maybe 200W of panels. We aren't talking about a house system or tops of RV's covered in panels. We're also specifically talking about the mppt75/15 and having 300W or 400W of panels connected to it (lets have them parallel and nominal 20V VOC) will not cause issues with it since it will limit its maximum output to a nominal 15A. Of course connecting more panel capacity than the controller can output will just be a waste of capacity.
Solar panels aren't quite current sources, they have an 'interesting' VI curve and that's why an MPPT algorithm works well to extra maximum power as the panel output varies with temperature,clouds,shading etc.
cheers,
george.