could there be two Davids onboard?

Ridley coully said in a Q&A that there are one or two androids aboard the prometheus, could it be that the second one is not Vickers, but a spare David. Maybe put on bpard as company for david when the others are in cryo? or to keep a 24hr eye on weyland? or maybe just as a spare. They don't take up a lot of room, would seem sillier not to take a spare (if theyre as handy as they say they are on the weyland site).