The group rule is not the law and so if the pilot exceeds the group rule he is not breaking the law ,eny one who sits in the aircraft has not got an instructor rating is a passenger.
So if your group insurance insists on 60 day currentcy it is leagal for a pilot who has not flown for 65 days to fly because insurance is not a legal requirement .When he has not flown for 90 days+ if he needs a checkout due to the group rules it must be with an FI as he cannot fly leagaly with a passenger.