They have no way of knowing because only the Holy Spirit knows who is genuine or not and HE'S NOT TALKING TO THEM because THEY ARE NOT.
We Do Not Know...
They seem to be moving to a more open confession that the F&D slave is the GB and not the anointed.
The F&DS are still the "anointed", although now said "anointed" have no special insight or extra Holy Spirit and are possibly nuts. In other words, just like your average dub except for destination. Apparently that doesn't apply to the GB however.