We revisit the "interpolating formula" proposed in our previous publication. It allows one to calculate the 0 nu beta beta-decay half-life for arbitrary neutrino mass without the involvement of the complicated results for nuclear matrix elements (NMEs) obtained within specific nuclear structure models. The formula derives from the finding that the value of a properly normalized ratio of the NMEs for the light and heavy neutrino mass mechanisms weakly depends on the isotope. From this fact, it follows, in particular, that the light and heavy neutrino mass mechanisms can hardly be distinguished in a model-independent way searching for 0 nu beta beta decay of different nuclei. Here, we show that this formula holds for all the known nuclear structure approaches. We give a mathematical justification of our results examining analytical properties of the NMEs. We also consider several simplified benchmark scenarios within left-right symmetric models and analyze the conditions for the dominance of the light or heavy neutrino mass mechanisms in 0 nu beta beta decay.