I never said that the type was known before runtime in OO. Your not a bug comment sounds awfully like an all bugs are features. Implementing static member functions this way would cause undefined behavior, which is a bug.
Yes it can. It simply means the subclass implementation has no access to a this pointer. When would undefined behaviour occur here? When a function tries to use a parameter that does not exist in the function signature, that's a compile time error not UB.
Maybe you think that, because a this pointer is needed for dynamic dispatch? A this pointer exists there, it is just not passed to the implementation.
Yes. My point is, that it can't be a static member function, because it's overridden by subclasses.