how many there in total where and how many were not discovered ?
Short answer is that nobody knows (or that nobody has researched them). Even the bodies have not been properly researched, to ascertain if they were undercover or not.
The 3 main sources of Intelligence men were
1. DMP, but as time went on they really did not enter the equation
2. Military Intelligence. Until Jan 1921 under control of Gen Boyd, after that moved to Police Control under Gen Tudor
3. Deep undercover men run by Basil Thomson - in effect MI6 in London
The Military Intelligence numbers of undercover men is estimated at from 100 to 200
Basil Thomson's men are particularly difficult to pinpoint as virtually nothing appears in the records (or has been deliberately removed). Molloy, Ryan, Fovargue, Digby Hardy (Gooding), Bell are examples of Thomson men
Effectively the IRA through the Castle moles, knew virtually all the names and addresses of the Military Intelligence men. And same for DMP obviously
Thomson ran his lot out of London to avoid Irish leaks, and to that extent was more successful in disguising the size of his operation