As I have pointed out before, Kodak uses about 200 fc for dye fade and Fuji uses about 500 fc for dye fade. These two tests mimic in one case the average home or museum and the other mimics average office environments. It is, in a sense, a reciprocity condition related to time vs intensity.

Kodak tested the conditions in thousands of homes across the world to come up with the value of 200 fc, and Fuji has tested many office environments to determine their value.

The ANSI committee is still out on this subject. Wilhelm uses Fuji's figures for light intensity IIRC. On top of this are the environmental factors of sulfur dioxide gas, and other pollutants that cause dyes to deteriorate. Add on humidity and temperature and experiments become very complex as does interpretation.

I have even seen a test in which short term stability of prints was worse than long term. The image was recovering with age for a reason that was quickly determined. Even so, this was not desirable, so the problem was solved and the product went out with the fix.