The non-unitary ideality factor of a MQW laser diode and its measurable threshold voltage are shown to be a puzzling question. The analysis is based on the predictions of the canonical rate equations, once they are translated into the device language, that replaces theoretical quantities as quasi-Fermi levels and carrier densities with measurable ones as voltage and currents. Trying the numerical fit of experimental curves, one is forced to go back to fundamentals of laser diode theory. The solution of the puzzle requires to reconsider points as fundamental as the meaning of locality of band-to-band transitions in quantum regions.