The registration number was pre-printed on the DP 1 card (Index Card). This number was assigned a single time to each DP when they first arrived in a DP camp. UNRRA and IRO employees in the DP camps of the British and US occupation zones later wrote the number on other cards. The DP 1 card was therefore the basis for all subsequent registration processes. Since the Index Card was given to the DPs as proof that they had been registered, there are very few of these cards held in archives.