So AD not really v big fuck la.
Not sure of the current numbers. In the 90s, there were 3. Likely to be more nowadays. In the past, you had DCPIB, DD CPIB and maybe 3 ADs. Now, you have DCPIB, Dir Investigation, Dir Ops and maybe Dir Admin. Below these Dirs, you have the DDs and I am sure many ADs will fall-in behind the DDs. Eric Tan must have copied the organisational structure of ISD.