Brother, with my apology, the information you have provided is either mediocre or stereotyped, because the recruitment process and posts etc are completely different than what u have presented.
People do not want to join ISI to become LDCs, UDCs and stuff like that.. there indeed are posts of clerks, Class-IV and administration, but they are usually taken from Armed Forces and are not directly inducted. The main emphasis stays on induction of Assistant Directors, Inspectors and Sub Inspectors...