Spoilers (bosses) (Sekiro: Shadows Die Twice)

If you killed the headless directly to him when he came, that is after the first memories and nothing more, is it possible to ring the bell for him? Do not say that there is more. Just if there is a shortcut to the plot - not. If there's some stupid side boss side location - you can. Without any spoilers please explain whether it is possible now to go or not.