People like to argue about the various archival value of various treatments, with an eye towards being able to know that if you use a specific combination of products, you'll be able to store your images for years to come.
Let's examine, however, what has happened so far in the world of art materials. People tend to assume that the various properties of materials are fixed, but the truth of the matter is that the only way we are going to know for sure is by either a pleasant or unpleasant surprise.
Marble statues were once archival. Now, if you let them sit in the acid rain, they decay. So, in order to know that a material is archival, you need to be certain that the pollution now is the same that the material is designed for.
It used to be considered acceptable to give an image a light selenium toning because it was thought that it would not change the colors very much but still protect the image. It turns out that if you use the latest formulation of selenium toners, this is not true. They didn't change the recipe, it's just that the contaminants in the commercial-grade ingredients the toner was formulated from changed and those ingredients acted as a weak sulfiding toner. So, this means that just because the fiber based papers of yore toned in Selenium have lasted until now, it doesn't mean you can rely upon this because, even if the recipe hasn't changed, you are not using the same materials that were used in the days of yore.
We make vague assessments from how things were, but people don't like to update their assumptions for reality. Kodachrome used to be significantly more archival than E-6 slides, but E-6 slides have improved so much that they now boast similar colorfastness. In fact, modern E-6 materials have less light-fading than Kodachrome. RC papers, when they were first introduced, didn't last. Modern RC papers have been reformulated specifically to not suffer this sort of problem, but the black and white art community hasn't changed the way they want to work.
How much care is put into your process also makes a difference. It turns out that you can both over-wash and under-wash the fixers out of a print. An ink jet print made with archival inks on paper that it isn't compatible with fade within years, whereas on compatible papers and compatible ink will result in a long print life.
Many digital formats have an unpleasant fade rate. Either they are perfect as the day you took the picture, or they are corrupted and unreadable.
Remember that basically all of the numbers that people give "300 year lifespan!" are extrapolated. The way it works is that they put it underneath 100 times the intended amount of light and then correct for 100 times less light. In 300 years from now, we'll know if they were right. In the end, there's no proven archival. We do the best we can and half the value of old pictures is that most of them didn't make it.