Hi Heather,
Usually discrepancies like the one you found are the result of mistakes in mapping software or, sometimes, mistakes by the local government that assigned street names and addresses. For example, a county assessor will report the address for a property as being on Hogue Mill Road, but when you're driving around looking for the house, the only street sign you see that looks close to that reads "Hogg Mill Road."
As another example, the property listing and the map software you're using to look up the location of a house for sale show the street name as Toliver Court. You drive to the area, and find no sign for a Toliver Court, but do find a sign for Toliver Drive. Near the end of Toliver Drive is a dead-end branch with no street sign. You drive along that, and find the house you're looking for.
I hope this helps. Any other questions, feel free to contact me. - Sun Dec 6 2009, 11:58