The engineering of new applications often relies on aca) Electronic mail: koopman@uni-potsdam.de b) Electronic mail: bargheer@uni-potsdam.de curate and easy-to-use models, which build up a correct intuition as they cover the essentials of the underlying physics and provide quantitative predictions. With respect to strong coupling in general, it has been pointed out that the most prominent features can be described with classical coupled oscillator models. Also in plasmonics, a rather simple electromagnetic model is often used to describe coupled systems: The excitonic material (loosely speaking "the emitters") is regarded as as an ensemble of two-level systems. Their optical response is modeled via a damped oscillator, i.e. a bulk medium is created that features a permittivity with a complex Lorentzian frequency dependence. Nanoparticles that consist of a plasmonic core and an emitter shell are typically modelled with classical electromagnetic tools like Mie theory or numerical Maxwell equation solvers. The increase and decrease of the real part of the Lorentz permittivity below and above its resonance leads to two opposing shifts of the original resonances: one to higher frequencies above and one to lower frequencies. This splitting is thus not explicitly included in the model but emerges as a result of the choice of material parameters as well as the geometry of the system. Experimental findings are typically modeled in qualitative , rarely quantitative 14 agreement. On the other hand, Antosiewicz el al. found that the model predicts a third peak between the two polariton resonances, when specific parameter ranges are met. It was attributed to a so-called shell mode where the Lorentzian coating attains metallic character (a negative real part of the Lorentzian permittivity). This spurious third peak, which also appeared in other published simulations, marks a clear contradiction to the usual models, as the masses-andsprings model or a simple quantum mechanical model for strong coupling predict only two polariton peaks. And experimentally, such a third peak has never been observed. This means, the aforementioned frequently used classical model may possibly lead to false intuition and false predicitons.