Why the wavenumbers are not stated on the reference spectrum?

It is not the policy of the European Pharmacopoeia to give the wavenumbers of the bands on the Infra-Red spectrum. There are, however, three calibration bands of the polystyrene film on the spectrum to help identify the bands of the substance. For confirmation of identity it is sufficient to show that the bands of the sample & reference spectra are concordant, ie they are both similar both in position & intensity (see General Method 2.2.24.)