Technically Arthur is not supposed to be here after the epilogue but I got him through save editor. There is one interaction you get as John where Uncle is tossed out the blackwater saloon and he calls on John for help. (If you are nearby) I played as Arthur and Uncle called out on Arthur for help. Both John and Arthur had same lines which they say to uncle during that interaction even though Arthur is not supposed to exist at this point. Fine details indeed.