Optical gain spectra presented for (Al,In)GaN laser diodes with lasing wavelength ranging from UV (375 nm) to aquamarine (470 nm) show a strong increase in inhomogeneous broadening, caused by Indium composition and quantum well width fluctuations which increase with Indium mole fraction. These gain spectra provides a standard data set for the calibration of microscopic many-body simulations. We demonstrate by comparison with basic simulations that the different assumptions of a global constant carrier density or of global constant quasi-Fermi levels for electrons and holes lead to a strikingly different dependency of optical gain on carrier density. For constant quasi-Fermi levels the threshold carrier density becomes insensitive to inhomogeneous broadening for realistic parameters. This is in agreement with the observation that the threshold current is nearly independent over the wavelength range from near UV to aquamarine.