@Sanguine
See my post #7 why their clearance is needed BY THE GOVERNMENT after agents/higher ups with secret information, knowledge of events, leave. Due to Bob's clearance and knowledge of names of our CIA agents, he was not allowed to go to certain countries for 20 years. One of those was Poland, where his ancestors came from and he would have liked to go there, but was not allowed. After all these years, he still cannot reveal certain knowledge - I don't ask what it is.
In the year before he went to the Pentagon, an active agent overseas turned and gave that country the names of CIA agents overseas - they were ALL killed.
Thanks, Marcella.
I heard a bit more on this question today. Apparently, this consideration is within the last 30 years and is only extended to a top few senior agency officials. Since it's the spooks, we don't know exactly when or by whom.
I suspect it is a tradition that may have just come to an abrupt end.
Regardless, why would an agent need clearance to tell the government what they already know? Also, they could be given temporary clearance if the were called back in for something specific.
And, of course, the success of this sort of thing would depend on the good character of the agent involved, something which appears to be severely lacking in this coven of bureaucrats.