Also think of this: as each subject was studied they were probably given a number, in case they were selected, and for easier referral when the higher-ups were discussing who to take. When the final candidates were chosen/taken, the numbers may not have been sequential. (for example, out of five candidates, the first, fourth, and fifth are selected and formally given the numbers 001, 004, and 005 instead of the numbering being changed to 001, 002, and 003. That way, if the candidates not selected were reconsidered, they could easily be given the numbers already associated with their file.)