FTIR and Raman are indeed complimentary techniques and for centrosymmetric molecules or unit cells there is the principal of mutual exclusion which means that a vibration can be either IR or Raman-active. In non-centro symmetric systems, however, this principle does no longer hold even if some transitions strong in the infrared spectrum show only weak Raman intensities and vice versa (and not all Raman vibrations become infrared-active). Now consider the structure of a glass... is it more related to a centrosymmetric structure or might it be non-centrosymmetric?

Glass is centrosymmetric and this implies that a vibration can only seen either in Raman or in FTIR. People used to find maximum phonon energy from FTIR and Raman. I feel that this makes maximum phonon enrgy value as a subjective result.

First of all, glass has a disordered structure... how can such a structure be centrosymmetric?! Second, have you ever compared IR and Raman spectra of glasses?...Then show us some examples where the principal of mutual exclusion holds...

Sorry I was mistakenly attributed the absence of even order optical nonlinearities in glass to centrosymmetric nature. As you mentioned glass is non centrosymmetric. Even if so, it doesn't assure that all the raman active vibrations will be IR active and vice versa. In such a scenario how appropriate the use of maximum phonon energy from any one of them. I'm attaching two references where you can find that FTIR and Raman spectra doesn't contain same peaks.

Well, I would suggest to you a more classical paper. In the two references you gave, IR measurements were made based on the KBr technique which is not the best possibility in case of inorganic glasses, where reflectance measurements are much more appropriate. Also, it makes sense to include results from neutron scattering in the discussion. Here it is: Article Comparison of the neutron, Raman, and infrared vibrational s...

Good hunt!