In Germany the government used census data tabulated on IBM punchcard equipment to find who to round up. Later, during the liquidation phase of the effort each camp had punch card equipment to help with maintaining the inventory of slave labor skills. That's what the number on the arm was for - the primary key. Copies of punched cards were sent to the central administrative HQ of the camp organization for additional processing and were used to identify specific skilled people who needed to be moved to other camps. Authoritarians rely on the stupid for the grunt work but they're not stupid themselves and can exploit technology to achieve their goals.