How you intend to fly the plane can make a big difference in CG. A plane with very light wing loading set up to fly 3D can have a CG that is much farther back than the norm. You know your way back when the plane wants to go into a harrier whenever you start to slow down. The CG range for a warbird is typically much tighter due to the higher wing loading and profile. Haveing the fuel tank on the CG can make a big differnce also, since you check it with the tank empty. One good point is that as you run out of fuel it should not change it too much. Also in many cases the recommended CG is very conservative (as in forward) to prevent bad results on the maiden flight.