Data on sales of previously owned U.S. homes from 2007 through October this year is likely to be revised down next week due to double counting, according to the National Association of Realtors. Many properties were listed more than once, the association says, and some new home sales were also captured in the data. Earlier this year, CoreLogic accused the association of of overstating results by as much as 20%. The bottom line - sales have been even weaker than previously thought.