The only thing that I would like to add is that Carbon dating is not used alone.
One of the key features of dating is that several methods are used, carbon dating, positional, relationship and correlation to other similar sites or objects, and all must be in agreement.
First, I don't think we or anyone else has a Nitrogen Bomb.
But what is actually looking at is the radioactive decay, where one isotope changes to another. That decay is very much at a fixed rate. The half life and decay rates are very precisely known.