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Recent developments on concentrated mixed crystal exciton spectra enabled us to develop new qualitative and quantitative empirical criteria for the identification of vibrational exciton splittings: Observation of an appropriately structured spectrum in the exciton band gap. This is especially useful for Raman Spectra where our previous criterion (the ideal mixed crystal $model1$) is not very useful due to the low intensity of dilute solid solutions and where the classical Davydov-Halford-Hornig-Mathieu polarization criterion is difficult to use, especially at low temperatures. The conflicting literature assignments of Raman exciton splittings for naphthalene are resolved: The 8 major splittings have all been missed before (using the classical criteria). The clarification of exciton splittings leads to some clarification of the normal mode assignments in the naphthalene molecule. A helpful criterion is utilized here as $well2$: Isotopic substitution has mild and predictable effects on the exciton band-width and splitting.