Counting runners at the start.

[fozzy]

Any number of my examples above that have the potential for double or mis-counting

This is why I favour the SI system - it reduces the mis-counting error - you must dib at each CP and the finish and download. And you can include an extra check at the start if required.

Barring technical failure (which is unlikely - happens very rarely at orienteering events) and idiocy, you will always get an accurate count. If necessary, it can be backed up with "traditional" paper recording as well.