I believe that rather than as part of periodic maintenance, the bone is used to tease deep scratches out of cordovan.
The bone is used to remove scratches from shell cordovan. Traditionally it's a female deer bone (Bambi's mum) as it has (allegedly) the right density as well as the required natural waxes. Try a bone knife (I believe cow bone), from a bookbinding supplier. Although I now have my own deer bone, I have previously found that a metal teaspoon works (almost) equally well. Hold teaspoon by the handle and plunge your thumb (for increased pressure) into the bowl. Apply a generous dollop of shoe cream to the scratch - the soft stuff, not wax polish - and rub the back of the spoon (sliding over the shoe cream) in circular motions over the scratch. Leave the shoetrees inside the shoe. After a minute or two, remove excessive cream and polish with brush. The scratch should be gone, or at least will be much better. Your basically repeating what the tannery has done, creating a surface with fat, rollers and pressure. For general maintenance, I hardly use any polish at all as that seems to be gathering and collecting in the creases. I usually lubricate with the ball of my hand, rubbing a bit of fat and sweat into the leather and removing at the same time any residue that might have collected in the creases. Then brush.