  We revisit the "interpolating formula" proposed in our previous publication.
It allows one to calculate the neutrinoless double beta decay
($0\nu\beta\beta$-decay) half-life for arbitrary neutrino mass without
involvement of the complicated results for nuclear matrix elements (NME)
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 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.
