Before revision: Rather than transporting hydrogen from Earth to use in making the methane and oxygen, they intend to mine the requisite water from subsurface water ice, produce and then store the post-Sabatier reactants, and then use it as propellant for return flights of their Starship no earlier than 2023.
After revision: Rather than transporting hydrogen from Earth to use in making the methane and oxygen, they have said they plan to mine the requisite water from subsurface water ice, produce and then store the post-Sabatier reactants, and then use it as propellant for return flights of their Starship no earlier than 2023.