Spectral complementaries only outside of crossover points. If only one response curve, cannot deduce color. So response curves must overlap. Further deductions possible by looking at wavelength discrimination, microspectrophotometry. Scrunched up colors at ends.
Colors match when the three responses of light are the same.
530nm green, and 650nm red. Cyan gives roughly same S and I responses, with half as much L response. Put more in green than blue, and get equal S and I responses. Hence, we need to subtract a little red. This shows that we cannot match all spectral colors with positive amounts of the three primaries.