My impression has always been that even on the darkest night outdoors and far from the kind of "light pollution" we now experience in most urban areas there is always more light than in a 100% blacked-out darkroom and yet if there is, then it might not be enough to fog film. On the BBC programme "The Genius of Photography" there was an interview with an American army photographer who during World War II has used a 35mm camera instead of the standard issue Speed Graphic. During the fighting in the Ardennes he had obtained chemicals from a shell-damaged chemist's shop and had developed, fixed and washed a roll of 35mm film outside in the dark using three soldiers' helmets for dev, fix and wash, hung the roll on a bush and had a perfect set of negs the next day.
Assuming his story to be true and I see no reason why its shouldn't have been, especially the part about having to wait until dark and develop it outside, then is there a very low level of light which allows film to be developed.?
It may be that a very dark night is in effect the equivalent of absolute blackness but I would have thought that even on the darkest of nights there must be more light than in a 100% blacked-out darkroom but presumably not enough to fog film but maybe still just enough for our eyes to discern a difference between 100% darkness and a very dark night.
Presumably some human eyes are better than others in the dark. Certainly an owl's eyes are. It can fly in conditions in which most or all humans would say that it was impossible to see.
Just a few thoughts and I hope you liked the story about the photographer. For our U.S. members, he had an Italian name which I cannot remeber but I think he was called Tony something and he continued to earn his living at photography after the war. Maybe someone here will know of him.