Looks like this should of be done ages ago.
So the method grade_object:insert override was done in March 2008 (commit '
MDL-12182 Fixing unit tests for gradebook. Mainly a change in set_locked() arguments. Merging from MOODLE_19_STABLE'). And then the only line that made that function different was commented few days later (commit message ' MDL-13899 feedback itself is a type of grading - date graded is now affected by feedback too; merged from MOODLE_19_STABLE'). So by the look of things this extra method could be removed ... in March 2008