Simplify the following text for a Grade 11 native English-speaking person.
Original: Because the notices of receipt for these parcels were often signed by other inmates , the ICRC managed to register the identities of about 105,000 detainees in the concentration camps and delivered about 1.1 million parcels , primarily to the camps Dachau , Buchenwald , RavensbrÃ 1\/4 ck , and Sachsenhausen .
Simplified: Because the notices of receipt for these parcels were often signed by other inmates , the ICRC managed to register the identities of about 105,000 detainees in the concentration camps and delivered about 1.1 million parcels , mostly to the camps Dachau , Buchenwald , RavensbrÃ 1\/4 ck , and Sachsenhausen .