> Anyone involved would long be dead or incapable of standing trial.
If, for example, some documents include details of spies in Russia never uncovered, even if those folks have retired/died, their network (and its recruited descendants) might well still be operating.
> Fair point, although I find it highly unlikely Russians or any indications of Russian involvement will be in here.
Doesn't have to be. "We asked source X at the Russian embassy if there was any indication they played a role" would still be highly sensitive, even if the answer was "no, not us".
If, for example, some documents include details of spies in Russia never uncovered, even if those folks have retired/died, their network (and its recruited descendants) might well still be operating.