The following methods all set _methods_annotations:
void set_method_annotations_of(int idnum, typeArrayOop anno)
  { set_methods_annotations_of(idnum, anno, &_methods_annotations); }
void set_method_parameter_annotations_of(int idnum, typeArrayOop anno)
  { set_methods_annotations_of(idnum, anno, &_methods_annotations); }
void set_method_default_annotations_of(int idnum, typeArrayOop anno)
  { set_methods_annotations_of(idnum, anno, &_methods_annotations); }

the last two setters should use the annotations matching the setter name.

The corresponding getters:
typeArrayOop get_method_annotations_of(int idnum)
  { return get_method_annotations_from(idnum, _methods_annotations); }
typeArrayOop get_method_parameter_annotations_of(int idnum)
  { return get_method_annotations_from(idnum, _methods_parameter_annotations); }
typeArrayMDOop get_method_default_annotations_of(int idnum)
  { return get_method_annotations_from(idnum, _methods_default_annotations); }

The setters are only used by jvmtiRedefineClasses.cpp.