Each concentration camp prisoner was assigned a number, known as their prisoner number, when they arrived at a camp. In the concentration camps, these numbers were more important than the prisoners’ names. During roll call, for example, prisoners had to report with their number instead of their given name. Sometimes the same number was assigned multiple times in the camps – after large numbers of prisoners had been released or transferred, for example, or when prisoners died. Furthermore, prisoners almost always received a new number when they were transferred to a different camp. An early overview of the prisoner numbers from 14 concentration camps can be found here.
Until February 1942, prisoner numbers were assigned multiple times in Mauthausen. The same number was sometimes issued up to six times there. If prisoners were transferred to an annex camp of Mauthausen, they would keep their numbers. Prisoners only received new numbers in Gusen concentration camp, which also belonged to Mauthausen. Prisoners who were transferred from Dachau, Buchenwald or Sachsenhausen to Mauthausen between 1938 and the summer of 1940 were another exception. They also kept their numbers from the previous camps. In Gusen concentration camp, this process continued for some prisoners until early 1941. It is not known why these prisoners kept their numbers from the previous camps.