Your will know your Spaceships' rego (registration or licence plate number) at pick-up.
We don't know your vehicle's registration (rego) beforehand as due to operational changes to the vehicles' allocation can happen regularly. See for more info about registration info for campsites or the ferry. Only on the day of pick-up we know with 100% which vehicle within the chosen category you'll be driving.
And for more info about the registration document.