A great deal of listing data comes from local MLS systems by way of ListHub. Sometimes, the original data is inaccurate, sometimes, it isn't transferred intact from ListHub. Sometimes, information like date built comes from public record and is auto-populated in the MLS. If it's wrong in public record, it will be propagated throughout.
I have it on good authority that ListHub will be out of the picture by the 2nd week of April, 2015. Trulia will be obtaining feeds directly from local MLS systems. Many inaccuracies will go away.
Emerald Estates Realty, Inc.
Palos Heights, IL 60463