This just shows that gchq have lost track of some of the criminals it knew about but had not gained enough intelligence to form a case (or the crimes were not considered serious enough). It has not lost track of the criminals that weren't using the communications channels it had a viewport on because it didn't have them tracked in the first place.
Seems like they became complacent and sat waiting for the evidence to appear in front of them. Rather than following up the leads in the old school methods.
Essentially: c+ must try harder.