The map was used by the US government   at the Potsdam conference, I don´t think the US government has any interest in falsification of true population numbers.
 Jews (those who survived) were grouped together with Germans in 1945 and that´s what was important for the US government ( see Michael Wieck)
 The map is the basis for the expected number of expellees, and 100 % is absolutely right for Lower Silesia.(84.139.198.229  )