A COM object class will inherit COM method implementations from its superclasses if no direct method is defined. However, unlike Lisp methods where an effective method is computed from the set of applicable methods for each generic function, COM methods are always inherited in groups via their defining interface. This is because the interface is used to call a COM method, not the COM object
Specifically, each method is inherited from the first class in the class precedence list that implements the interface where the method is declared. No attempt is made to search further down the class precedence list if this class is using the unimplemented method definition described in Unimplemented methods.
LispWorks COM/Automation User Guide and Reference Manual - 19 Dec 2011