The editing and fact checking on these books are atrocious. I have a few more goofs if you want to list them. 

1)When Lily and Tommy start on their journey south for the long supply run, they begin with a 3/4 full tank of gas, drive straight through, and run out of gas. This means they likely travelled somewhere around 200 miles away from home. Yet they manage to walk all the way back to the tunnels before dark the same evening, even though it was already late afternoon when the tank ran dry. 

2)The tow truck that Lily and Jeremiah ride in tips onto its right side. Yet a few pages later, Lily is again driving the same tow truck without any explanation for how she tipped it back on its wheels by herself.