  Neutrino mass sum rules are an important class of predictions in flavour
models relating the Majorana phases to the neutrino masses. This leads, for
instance, to enormous restrictions on the effective mass as probed in
experiments on neutrinoless double beta decay. While up to now these sum rules
have in practically all cases been taken to hold exactly, we will go here
beyond that. While the effect of the renormalisation group running can be
visible, the qualitative features do not change. This changes somewhat for
model dependent corrections which might alter even the qualitative predictions
but only for large corrections and a high neutrino mass scale close to the edge
of the current limits. This finding backs up the solidity of the predictions
derived in the literature apart from some exceptions, and it thus marks a very
important step in deriving testable and robust predictions from neutrino
flavour models.
