Certain areas on old guns wear to a high sheen, and others keep their scuffs and scratches and collect dirt. Wrist, forestock grip, comb, patchbox side of butt, and ridge of cheekpiece all get the most wear(and polish). Areas that don't get much wear are:ahead of the lock panels, behind the cock, under the cheekpiece, under the grip rail of the guard.
When you scrub the stock with coarse paper, scotch brite, natural wear from use, carried on horseback, pushing your way thru the bushes, all those areas will naturally get aged and worn appropriately.