So, the values in the graph are computed as follows?
The values from the camera for each channel (R, G, B) range from 0 (no light) to 255 (maximum light). For graphing, these are scaled between 0 and 100 (e.g., by dividing by 2.55) and a graph of each channel can be seen under "More Tools/Toggle RGB." To combine these three channels into a single value for each wavelength (or wavelength bin), the three percentages (the R, G, and B for each wavelength) are added and divided by 3 (or the camera values are added and divided by 7.65).
So values in the combined graph can exceed 33 without any of the camera values being close to 255. For example, camera values of 160, 140, and 20 will be graphed at 41.8 (320/7.65).
If a laser source with a value of 254, 0, 0 is graphed at 100, then an equally bright line at 590 nm (where the red and green channels overlap and the values could be 180, 180, 0) might have to be graphed at a value greater than 100.