The Arolsen Archives have what they refer to as “number card files” for almost every concentration camp. These are not historical number card files from the camps, however, but card files put together by the ITS. The ITS began creating these card files in 1950 as finding aids so that people could be identified on the basis of their prisoner number. Cards in the Central Name Index (CNI) were used for this, which refer to documents that mention the person and his or her prisoner number. This card file that the ITS created as a tool reveals how often the same number could be assigned, as these examples from the Buchenwald collection show. In Buchenwald concentration camp and its sub-camps, prisoner number 3 was assigned to Fritz Siekmann as well as Kurt Witt, Martin Janischka, Rudolf Arlt, a prisoner referred to only as Coninche, Iwan Sysranzew, Karl Egyde, Minna Rathmann and possibly others.