I assume so. The folks that designed the scanners were no slouches. I suspect that they never completely turned off any LEDs, so there was always some deliberate “slop.” With LEDs, however, you can explicitly control that. They probably had some kind of filter, also. I never took one apart, though.

I got the response curves by feeding in a special slide with a diffraction grating.

The curves were markedly different from an incandescent light source.