C-c prefix is supposed to be "reserved" for end-users. But the sad reality is that more than several major-modes break the convention by overriding C-c ... . So I no longer use C-c prefix and instead define my own keymap.
It is more secure, at least probabilistically speaking.
Actually, I even append a hook to after-change-major-mode-hook so that important local keybindings will never be taken by a major mode.