The Schechter-Valle theorem states that a positive observation of neutrinoless double-beta (0 nu beta beta) decays implies a finite Majorana mass term for neutrinos when any unlikely fine-tuning or cancellation is absent. In this note, we reexamine the quantitative impact of the Schechter-Valle theorem, and find that current experimental lower limits on the half-lives of 0 nu beta beta-decaying nuclei have placed a restrictive upper bound on the Majorana neutrino mass vertical bar delta m(nu)(ee)vertical bar < 7.43 x10(-29) eV radiatively generated at the four-loop level. Furthermore, we generalize this quantitative analysis of 0 nu beta beta decays to that of the lepton-number-violating (LNV) meson decays M- -> M'(+) + l(alpha)(-) + l(beta)(-) (for alpha, beta = e or mu). Given the present upper limits on these rare LNV decays, we have derived the loop-induced Majorana neutrino masses vertical bar delta m(nu)(ee)vertical bar < 9.7 x 10(-18) eV, vertical bar delta m(nu)(e mu)vertical bar < 1.6 x 10(-15) eV and vertical bar delta m(nu)(mu mu)vertical bar < 1.0 x 10(-12) eV from K- -> pi(+) + e(-) + e(-), K- -> pi(+) + e(-) + mu(-) and K- -> pi(+) + mu(-) + mu(-), respectively. A partial list of radiative neutrino masses from the LNV decays of D, D-s and B mesons is also given. (C) 2016 The Author(s). Published by Elsevier B.V.