Having worked for a map company for 8 years, I can tell you that the only non-existent streets that have found their ways into our maps come from other sources, like city planning plats, and the only towns that ‘aren’t there’ are dead post offices, like Maces Spring, Virginia, or things that made their way from other sources, like a database of ‘towns’ from trucking management that included some client-specific drop points.
I should add that mapquest will never tell you it didn’t find a town - failing all else, it will put you in their arbitrary center for a state, or 100 degrees West by 40 degrees north, their arbitrary center for the U.S.