I made a post that described the effect of illuminant on film response as a function of wavelength. This is exactly what you describe and is well known in the industry. I did not reference your paper. I was using facts from my own background.
This is a general problem when one uses a narrow band illuminant to test a film or paper. It gives results that vary as much as you show in your graph or even more.
This error can lead one quite far astray.