maybe they not wearing maybe they just shining up like that barrel of Kurts??
But its common to move to a thicker patch after a few hundred and to go up one ball size (.490 to .495) at about the thousand mark.
One bloke showed me a CVA mountain rifle that had documented over 3000 and he was shooting a .50 ball on calico patch - said that gun had started out at a .490 ball on calico.
it takes real dedication to put big miles on a muzzleloader.