I am however not too sure about getting the second part of your question right. Do you mind elaborating a little? Thanks!
I assumed all possible conversions have been considered before the mass of particles such as electrons et al were estimated. Now that we are proposing a mass of neutrinos, the mass needs to be accounted for somehow.
I don't know if I making any sense.
If we saw; A + B = 6
and we also say, A+B+C = 6
It means that C = 0, right? Now, if we say that C is not 0, then A+B cannot be equal to 6.
I don't understand your reply... sorry :D
Maybe the clarifying point is that neutrino masses are tiny, but non zero. Therefore, in many phenomena, the precise value has no effect (because it is negligibly small). We need to look at the right observable to get the impact of the mass visible, like neutrino oscillations. There without a mass there is no oscillation whilst with a mass there are oscillations. This cannot be missed.