I have to say, PE, that that is rather fascinating what you just said about the safe being 'safe for paper' but not necessarily safe for color film. Indeed, one wonders for just how long the paper safe is 'safe for paper' since you confirm that, indeed, some theoretically tiny amount of 'light' actually might get into the safe and, of course, can accumulate. Boy, is B&W a different way of thinking about things such as this! Aside from the fact that the paper has no, or low, sensitivity to red, one really wonders if any light accumulates to fog, albeit slightly, eventually even the paper. I am so tied to 'if you cannot see it, it does not exist' and this is just plain wrong on my part.
Ignorantly, I had thought that the paper safe was safe, period. There are qualifiers which necessarily must go along with that truism. I have to admit, again, that this experiment has opened my eyes a lot, even after 48 years in the darkroom. And to hear that said by someone like yourself and for me to witness the actual veracity of that fact is compelling. Sorry for the emotion here but that is revelatory. Not so often is that fact experienced but it does exist.
What if I made a statement such as this? Age fog is caused by photons entering and passing through light-tight packaging. Even the most dense, 'light-tight' material will allow a few photons to cross its threshhold. This accumulates slowly, very slowly, but it happens and results in slight base density, perhaps only after several years' time.
And BetterSense: that finding on your part is interesting. I have no answer for you but I assume that both films, the one sealed and the one not sealed, were kept in the same package, so that there is no chance of other factors entering into the equation. Or I wonder if light had a 'better' opportunity to enter onto the unsealed film. - David Lyga