Beginning in the third quarter 2011, the CPS/HVS began revising earlier housing inventory estimates, based on the latest independent housing controls available. The revisions are based on the latest vintage year, where independent housing controls were available. For example, vintage 2009 means that all of the estimates in this time series are identified as belonging to "vintage 2009." The 2000 data are from the 2009 vintage, the 2001 data are from the 2009 vintage, and so on.