A car not being seen does not mean one did not exist. How often do people not notice the obvious? Or, if someone turns their back for a few moments, do we have universal awareness? No. The absence of a reported vehicle does not mean one did not exist. If they were on foot, who knows? But to discount a thing because it was not observed brings into question the condition of the event relative to the observers. If someone is in a guard tower with a note pad, that is one level of awareness; if someone is just working around the house and they do not see something, that is at a lower-level of awareness. The condition of awareness at the time of an event is a factor in eye witness reporting.