Perhaps one additional point to stress: transformations that normally turn particles into their antiparticles turn the Majorana neutrino into the identical state, just as for photons. So one could not say that neutrinos have one chirality and antineutrinos have another, because there would be no such thing as antineutrinos, there are just two different chiral eigenstates.Let me summarize it again. I hope I get it right.
For Majorana neutrinos the only difference between "neutrinos" and "antineutrinos" is the chirality. Neutrinos are left-handed and antineutrinos are right-handed. There are no other "charge-like" quantities like lepton number. In other words: For Majorana neutrinos the charge-conjugate of the left-handed neutrino is the right-handed neutrino and vice versa. Since there's no "lepton number" there's also no lepton-number conservation.
Not sure what this means. Since pure Majorana neutrinos have zero lepton number, or no lepton number which seems like more or less the same thing, when an electron strikes a proton and makes a neutron and a Majorana neutrino, which is involved in neutronization in supernovae, lepton number violation is dramatic to say the least.The lepton-number violations in the case of Majorana neutrinos are small due to the smallness of the neutrino masses.
So it sounds like the answer to how they know to make leptons or antileptons is chirality, but not lepton number, and not particle vs. antiparticle.A very concise treatment is in the Book
S. Bilenky, Introduction to the Physics of Massive and Mixed Neutrinos, 2nd Ed., Springer (2018)