The different numbers on the plaques can possibly be explained in this way : Auschwitz was not the only concentration camp. The first plaque attributed 4 million deaths to the one camp, Auschwitz, when actually other camps, as well as Auschwitz, were responsible for the higher number. The difference between the higher number and the 1.5 million can be accounted for as the more specific number of deaths due the one camp, Auschwitz.