Get Unique Values when doing Select by Attributes returns all unique values from the entire layer rather than from the data specified by the Definition Query in the layer’s properties.
Possible workaround (no better workaround, need to do some extra work compared with NON in 9.1)Option 1:After setting up the definition query, label the attribute field so that the user can see all the values. Then perform the Select by attributes if the user still needs to do so.Option 2:Export data for the selected (or definition queried) state as individual shapefile/feature class and edit the new data. Then use the Append tool to append all the state shapefiles/feature classes together if necessary.